To be fair living things have a lot of in built safety measures. We learn sharp things and fire and etc are dangerous. So even if we gained immunity to such objects it would take a while to get used to and would require testing and confirmation to adjust to.
Also the idea of strong and weak in his mind is different to the idea his elf has. He also knows he is strong now, but he can't really tell his own strength or what that means. He felt nothing from blowing the moon up after all so normal stuff is obviously not worth mentioning. He messed up because his expectations and the rest of his mindset are still in the other japan world. He is not yet ready to live in this world and to be fair he has only been here a little while and was stuck in a cave for most of it.
Some people might adjust immediately using logic, sure. Many however would flail around fish out of water style through atleast 2 or 3 encounters before coming to realize the new status quo and adjusting.