made a video talking about this. dont use your legs to lift more weight, to build a bigger chest. what sense does that make? plus, doesnt count in competition OR give ANY muscle building benefits. Sorry to hurt anyones ego.
Arching your back and using leg drive are both allowed in powerlifting competitions. Having your feet flat on the floors are actually part of the rules in a lot of competitions. Extreme arching has been removed in some competitions but arching in general has not.
That was in regards to your comment of it doesn't count in competitions ^. In terms of building muscle, I would argue it reduces your risk of injury to have a slight arch in benching. Will that take away from some of the humerus adduction that is a function of your chest? Sure, but your shoulders are going to be in a much more risky position with 315 in your hands vs having a higher chest with your shoulders back.
Hope that didn't come off in a negative way I was just debating your POV based on my experience, studies and other trainers that are known around in the mechanics of hypertrophy training such as Mike Israetaeli, Layne Norton, Mike Van Wyck and Justin Shier.
If anything, I always encourage conversation around these topics. There are pros and cons, but I feel the cons outweigh the pros, considering most of the time the pros are only ego based. You are correct in regards to the shoulders. But yes, I will say, arching isnt as bad as some people say, sure, but I still think my opinion is valid. A slight arch can actually be super useful though, like at the end of some of those later more tougher sets on the very ends of the sets/reps ect, but even then I would highly suggest not having such an extreme arch like MAJORITY of people who follow any random advice they see online. Not saying its my way or no way either bro. You got some good points.