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I am adding a new answer because I don't believe any of the other answers have fully addressed a key component of the your particularly situation: that you are suffering from Imposter Syndrome.

This is evident by the statement:

I have the role of the tech lead / architect of the team, though I have less experience both in general and in this project than one of the freelancers

The Imposter Syndrome is likely the reason why you had an emotional reaction to your coworker's demands to get involved with the perf testing, and likely holds the clue for how you can easily deal with this kind of behavior.

The key to this is the recognition that the sufferer of imposter syndrome almost always oversimplifies a complex situation to their own detriment.

In your case it may be an assumption at some level that you are unequipped to take technical leadership of the team because you are less experienced or skilled than other team members.

If this is the case then you should recognise that to provide good leadership, soft skills like communication, political awareness, empathy, and organisational capability far outweigh hard skills, and that you would not be in the position you are in if you did not posess these to some degree, and it is therefore perfectly normal and reasonable for you to be responsible for the team's technical direction and to make such decisions as to further the outcomes that you believe are correct.

I am adding a new answer because I don't believe any of the other answers have fully addressed a key component of the your particularly situation: that you may be suffering from Imposter Syndrome.

This is evidenced by the statement:

I have the role of the tech lead / architect of the team, though I have less experience both in general and in this project than one of the freelancers

If true, the Imposter Syndrome is likely the reason why you had an emotional reaction to your coworker's demands to get involved with the perf testing, and likely holds the clue for how you can easily deal with this kind of behavior.

The key to this is the recognition that the sufferer of imposter syndrome almost always oversimplifies a complex situation to their own detriment.

In your case it may be an assumption at some level that you are unequipped to take technical leadership of the team because you are less experienced or skilled than other team members.

If this is the case then you should recognise that to provide good leadership, soft skills like communication, political awareness, empathy, and organisational capability far outweigh hard skills, and that you would not be in the position you are in if you did not posess these to some degree.

It is therefore perfectly normal and reasonable (although it may not feel like it) for you to be

1. responsible for the team's technical direction, and
2. taking such decisions that you believe are correct for the team

I am adding a new answer because I don't believe any of the other answers have fully addressed a key component of the your particularly situation: that you are suffering from Imposter Syndrome.

This is evident by the statement:

I have the role of the tech lead / architect of the team, though I have less experience both in general and in this project than one of the freelancers

The Imposter Syndrome is likely the reason why you had an emotional reaction to your coworker's demands to get involved with the perf testing, and likely holds the clue for how you can easily deal with this kind of behavior.

The key to this is the recognition that the sufferer of imposter syndrome almost always oversimplifies a complex situation to their own detriment.

In your case it may be an assumption at some level that you are unequipped to take technical leadership of the team because you are less experienced or skilled than other team members.

If this is the case then you should recognise that to provide good leadership, soft skills like communication, political awareness, empathy, and organisational capability far outweigh hard skills, and that you would not be in the position you are in if you did not posess these to some degree, and that this qualifies you to be responsible for the team's technical outcomes and take decisions to further them.

I am adding a new answer because I don't believe any of the other answers have fully addressed a key component of the your particularly situation: that you are suffering from Imposter Syndrome.

This is evident by the statement:

I have the role of the tech lead / architect of the team, though I have less experience both in general and in this project than one of the freelancers

The Imposter Syndrome is likely the reason why you had an emotional reaction to your coworker's demands to get involved with the perf testing, and likely holds the clue for how you can easily deal with this kind of behavior.

The key to this is the recognition that the sufferer of imposter syndrome almost always oversimplifies a complex situation to their own detriment.

In your case it may be an assumption at some level that you are unequipped to take technical leadership of the team because you are less experienced or skilled than other team members.

If this is the case then you should recognise that to provide good leadership, soft skills like communication, political awareness, empathy, and organisational capability far outweigh hard skills, and that you would not be in the position you are in if you did not posess these to some degree, and it is therefore perfectly normal and reasonable for you to be responsible for the team's technical direction and to make such decisions as to further the outcomes that you believe are correct.

I am adding a new answer because I don't believe any of the other answers have fully addressed a key component of the OP's situation: that they innately believe at some level that they are unequipped to take technical leadership within the team, because they are less experienced or skilled than other team members.

I once worked on a team as a developer where we got a new technical lead, who was a Vendor MVP and had published much highly regarded technical material. However, he was adversarial, disorganized, and had no ability to empathize. The team's ability to deliver value fell off a cliff. He eventually left and the team started delivering software again. The other developers on the team, like myself, didn't care that he was by far the most technically skilled person.

I joined another team where I was the most junior member both in terms of skill and experience, by a lot. After a few weeks of joining I realized that the team was not building what the stakeholders wanted, and also was not delivering to time and budget. I spoke to my teammates about my concerns, then our manager and stakeholders, and was lead developer on the team soon afterwards. The other developers didn't care that I was by far the least technically skilled person, because the team was delivering and the stakeholders were happy.

In my current team, I am technical lead despite having written no code for over 12 months. I got a new work laptop recently and I didn't even install the IDE. My job is to be responsible for the technical outcomes, so I ensure the other developers in the team are working on the right things, progressing in the right direction, with the right assumptions. I have some very strong developers in my team, who all look to me for technical leadership, and none of them care that not only am I the weakest developer on the team, I don't even code.

The point is that you don't need to be the most experienced or skilled to lead a technical team, in fact it is my opinion that it is better for team productivity if you are not, as you want the strongest developers writing code, not doing all the other thankless crap that a lead developer needs to do. You just need to be able to communicate better, organize better, make better decisions, and obsess on delivering the most value in the shortest amount of time.

I am adding a new answer because I don't believe any of the other answers have fully addressed a key component of the your particularly situation: that you are suffering from Imposter Syndrome.

This is evident by the statement:

I have the role of the tech lead / architect of the team, though I have less experience both in general and in this project than one of the freelancers

The Imposter Syndrome is likely the reason why you had an emotional reaction to your coworker's demands to get involved with the perf testing, and likely holds the clue for how you can easily deal with this kind of behavior. 

The key to this is the recognition that the sufferer of imposter syndrome almost always oversimplifies a complex situation to their own detriment.

In your case it may be an assumption at some level that you are unequipped to take technical leadership of the team because you are less experienced or skilled than other team members.

If this is the case then you should recognise that to provide good leadership, soft skills like communication, political awareness, empathy, and organisational capability far outweigh hard skills, and that you would not be in the position you are in if you did not posess these to some degree, and that this qualifies you to be responsible for the team's technical outcomes and take decisions to further them.