I guess I have to say this again:
The most common criticism people have said about Superman for years is that he's "boring and overpowered".
Corenswet's Superman is meant in part to combat that criticism. Corenswet's Supes is still strong but he's not invincible and faces some challenges. There's literally nothing wrong with that.
Also, ONCE AGAIN, in the movie it's not like he was getting beat up by some random average man. Ultraman is Superman's equal in strength and power. Of course, it's not going to be a walk in the park for Superman to defeat Ultraman.
This is really simple stuff and I don't know why this is so hard for some of you to understand