I'm not an engineer but I rather appreciate the untested = bad mindset from the people who would potentially design one of the many devices that could kill me if they malfunction.
I see that there is one complaint missing from your question, so I'll ask it here: is work being done on time? If not, you have a legitimate grievance. But if that were the case I suspect that it wouldn't be missing from your description of the situation, so I'll assume that you don't miss any deadlines because of that.
Conflict is Good
With that in mind, here is my answer: Change nothing. Embrace the debate, learn to stand up and fight for what you think is the best overall solution. Your ideas got accepted because you convienced the team that they would. This is part of your training, you should treat it as such.
If you don't set a meeting agenda before hand, start with that. Then you can do your research on each topic that you want to propose a solution on and prepare for it as if you were preparing for a debate. Yes it's a lot of work, but did anyone say engineering was easy? If anything you might change your mind in the process. Now when you fail to get your own way you'll know it's because your idea or your defense of it wasn't good enough, and fix it next time around.
...but sometimes unnecessary
On the other hand I accept that sometimes you just have to make a mock of the gizmo and not the gizmo itself. Then you must convience your opposition of the importance of scoping It's a proof-of-concept and (if applicable) doing it the "bad" way gives us time to do {awesome thing}. If testing a sensor can be done realiably with a solderable breadboard, you don't have to make a dedicated PCB for the thing (scope creep). If Arduino is easy and available and the "pure" solution costly and time-consuming, there's no need to go pure. I understand engineering to be the art of compromise, if nothing else. Complexity breeds complications, and the KISS principle should be observed at all times. These are your arguments.
A related question deals with this situation when arguments happen just for the sake of arguing (which doesn't sound like your thing but I'll leave it here just in case): How to handle a coworker who likes arguing to cause conflict.
