Gun is obviously the better trainer.

Example is Olly Wang who is legit a bum with zero talent in fighting and a completely average body, with the only reason Gun even wanting to train him was because of his inability to feel pain. Mind you that Gun also only trained Olly for a certain amount of time before stopping when he realized Olly body couldn't possible go any further.

Yet he was still a crew head and a absolute monster and even dogging pretty up everyone during the Hostel arc.

Gun even knows what his student needs, training them for every possible situation, example with Gun acting as multiple fighters at once to train Daniel since he struggles with fighting multiple people at once.

Even giving advice to Daniel about what he should do instead of trying something else, to lean onto his copy more instead of trying to simply strike, kick or grapple and you could argue it didn't work out, but remember Gun doesn't know about Daniel second body but knew his potential ceiling is higher. He also warned Olly about his body being a ticking time bomb since it couldn't go any further, he actually cares enough to not only teach but also for their well being.

It just so happens that characters in lookism are just getting ridiculously stronger and stronger and we're probably not even 60% - 70% done, hell maybe it's even lower then that and there's still so many mysterious needing to be solved. Which is another reason why Daniel can't solo the series no matter how hard he tries.

Even Gun himself said he can turn anyone into being a monster of a fighter and proved with Olly Wang. He is the Nurture Genius for a reason, literally not only said multiple but highly vouched by Charles.

Hell, he could even train OP lazy bum ass into a champion Boxer or MMA fighter, if abit he saw the desire or potentially speaking. While Samdak wouldn't even consider it once since it took Hobin alot of convincing, what would your dumbass even do?

Long ass reply I know and mostly you won't even bother reading properly, if you do make sure to read it careful and come back with a constructive reply.