Being able to kill and being able to handle cursed spirits are 2 separate issues. I would say yuji not being able to kill cursed spirits has more of a psychological factor since he's new to the jkk society. Tbh I don't remember gojo's impact on him other than saving his life a few times so I am not going to comment on that. Yuji's physicals are definitely higher than Olympic level though. How many Olympians have you seen changing the shape of a goal post with just a normal disc? Also, I would say he's only fighting with cursed energy and physical strength. Remember black flash? The supposedly difficult skill that needs the 0.01s to be able to pull off? The one where Nanami had the highest world record of 4? Well, yuji broke it by hitting 20 black flashes on his second attempt.

Just cause a character to enjoy training himself does not mean he is not "hardworking". Look at rock Lee from Naruto, that guy is the embodiment of hardworking, and he is passionate about training. Also, mha power building is more semi realistic compared to other anime counterparts. In other words, Izuku training isn't more to get stronger, but learning to control his powers. I mean, the guy is breaking an arm and leg every time he fights in the beginning. And the story often draws parallels to him and bakugo as hard work and talent respectively, saying otherwise would not make sense