Personality traits are often observed and confirmed through subtleties in your behavior, and I suspect you're oblivious to those subtleties. Just as an example, I'm going to dissect a single sentence from your question:
my boss, which I consider a really capable and smart manager, has a system for measuring developer performance, in which I constantly get much more points than the second best developer
- Considering your boss "smart and capable" is perfectly fine, but it:
- does not matter in relation to how your coworkers feel about you
- comes off as incredibly biased and/or manipulative since you then continue on mentioning that you personally do very well in your boss' evaluation
- is only being used as further justification of why this evaluation that puts you in first place is supposedly a really good evaluation metric. It's not intended to compliment your boss, it's intended for you to indirectly self-aggrandize.
- Why point out that you constantly do better?
- Why point out that you do much better?
- "I do better than the second best" is subtly trying to say "I'm the best" without outright stating it.
These are all red flags. A more humble person, even when getting the same evaluation as you, would've stated something along the lines of:
I've received positive feedback in these evaluations
And when you go on to read the rest of your question, this is really the purpose of that paragraph: telling us you score well on the evaluations.
The rest of the way you phrased it doesn't add anything of value, but it adds a whole lot of boasting, mutual favoritism, and reveals how much you focus on separating yourself from others competitively. In other words, you've basted your message in arrogant sauce.
I'm trying to be more passive
Your boss didn't ask you to be passive, he asked you to be inclusive of others' opinions. The fact that you think that the only way you can contribute is by stifling others' input (or else be passive) is a worrying sign.
I feel like I'm walking on eggshells
Another red flag. You're asked to include others in the discussion, and you perceive this as if you're now having to carefully handle these "fragile" coworkers.
This just goes to show exactly how much you prefer cutthroat competitivity (being the best) over mutual cooperation (working together).
specially when debating topics in which I'm specialized and where is not possible to have a "middle-ground solution"
You're still missing the point. Including others in a discussion does not equate to forced compromise. It means that you need to hear everyone's concerns and thoughts before making a decision together.
Even if your solution is objectively the better one, that does not prevent you from listening to your coworkers' input, discussing the pros and cons of each different approach, and then cooperate on deciding what steps to take.
If your argument is correct, then the exploration of the pros and cons will prove that point, which is going to sway opinion in favor of your solution.
But if you come in heavy-handed, ignoring others' input and immediately proclaiming to already know the solution, then you're going to meet a tremendous resistance to doing things your way. You catch more flies with honey than vinegar.
I also feel some "negative vibes" from some of my coworkers when communicating.
I'm not surprised. Even in your question, where your have the benefit of us only hearing your side, your arrogance and lack of cooperative spirit already oozes through. I can only imagine how much clearer that picture gets in the context of being your coworker every day.
Those negative vibes you get are bouncing back off of your coworkers. You negatively interact with them, and so they negatively interact with you. You can't blame the mirror for being ugly.
I refer back to the eggshells comment. You're repeatedly implying that you have to unfairly dial yourself back, simply when you are asked to cooperate and respect everyone's input.
is leading to design by committee problems in some of our projects
"Design by committee" refers to cases where everyone does their own thing without much coordination or forethought.
You are being asked to coordinate with your coworkers. You're not being asked to design by committee. You're being asked to not design by dictatorial rule.
Note that in my team there aren't any tech-lead / software architect positions.
And what gives you the idea that you, with your 6 months of seniority, get to therefore usurp the leading position?
And that's not even mentioning the fact that leaders should not call shots, but coordinate others to call shots. Even if you take that leadership position, you can use that position to ensure everyone's input gets heard, instead of ensuring that everyone hears your input.
Leaders are elected by their citizens, not by self-proclamation or a power grab. You're trying to be a dictator (quite literally: someone who dictates the solution), not a leader.
Note that I'm very assertive and competitive by nature
This is just "I want to behave the way I want to", wrapped in some bogus justification that it's allegedly your "nature" and implying it's normal.
It always looks like healthy competition when you feel like you're winning.
"healthy competition" between colleagues
If the word "competition" comes to mind before "cooperation" when thinking of your coworkers, then you are a troublesome coworker.
Is there a way to effectively debate technical ideas, in an assertive way, without being perceived as arrogant?
"To assert" means to state something as a fact, forcefully. It is the exact behavior that is causing you to receive this negative feedback from both your coworkers and your superiors.
Asking how to keep doing the thing you're being told not to do, based on your self-perceived notion of superiority, is the pinnacle of arrogance. What you're asking is no different from asking how you can punch someone without being perceived as violent. The exact thing you're trying to do is the thing you're being accused of.
The opposite of arrogance is humility. It entails not always thinking (or arguing) that you're right, instead being open to what you observe / are being told, instead of what you think about yourself. Second-guess yourself. Listen to others' input. Don't try to persist your ideas above all else. Assume you are not a perfect being.
Your boss' feedback was spot on. Mellow out (i.e. don't see your coworkers as competitors), listen to others, stop trying to claim the spotlight or leadership position.
Here's another way of looking at it.
You are being a bad communicator. This is clear both from the feedback you are getting and the way you yourself think you should be interacting with your coworkers.
Cooperation and communication are key skills for any employee, most certainly a developer. So if you're a bad communicator, that makes you both a bad employee and a bad developer.
Since you're so competitive (one might even say it's in your nature), shouldn't you then be trying to be a better communicator? So why are you resisting?
If you want to argue your own worth based on adhering to your manager's metric, a manager who you claim to be smart and capable; then you should also be listening to your manager's feedback on how you are behaving and how you should change how you treat your coworkers.
Competitive people want to be better. So work at being a better coworker, instead of arguing why you shouldn't need to be or trying to persist the same behavior you're being told to stop.