but wouldnt the muscles grow more if i take more weight and support my back with a bench
proportionally to your sholders yes
but by standing your growing your legs abs and lower back maybe even some calves but of course sholders and tri's and traps would grow the most proportionaly. but thats the reason why you would have to use less weight standing because your legs and secondary groups get fatigued aswell
youll grow either way
but it would be
all sholders tri's and traps sitting down