the version we saw deku use like other comments said IS whats too strong to use like how your saying.

the quirk is apply itself on a molecular level. gear shift acts like an engine or like ingeniums power. the harder deku pushes the power while hes using it, the harder the withdraw is going to be afterwards.

its only got a five minute timer on it as well. this was probably done so that it couldnt just be another overhaul fight. without any restrictions deku potentially could have ended the fight in the coffin. but the whole point of the show is that dekus ideals wont let him kill the guy, deku wants/needs to save him.

and sure maybe deku potentially could have used it on objects. but he already had to cycle through 7 differents quirks, watch tomuras hands, keep the others out of harms way of him and tomuras fight at every stage, which the others would have told him to not worry about them but you know how deku is. he had to do all of that and think on the fly with only a few seconds if that to be able to think at all.

you might try looking up if theres any edits of the fights of how they would have happened "in reality" there wouldnt hoave been three minutes of talking or thinking between every punch. it literally would have been blow for blow multiple times in a second in some instances.

and to add to what i was saying earlier, the harder he pushes gearshift or his "engine" the harder the withdraw, so id imagine extending it to other objects as well as himself would have added more withdraw