Superman has never been weak, and that's the issue. Making him look weak is directly contradictory to his character.

"𝘐 𝘧𝘦𝘦𝘭 𝘭𝘪𝘬𝘦 𝘐 𝘭𝘪𝘷𝘦 𝘪𝘯 𝘢 𝘸𝘰𝘳𝘭𝘥 𝘮𝘢𝘥𝘦 𝘰𝘧 𝘤𝘢𝘳𝘥𝘣𝘰𝘢𝘳𝘥, 𝘢𝘭𝘸𝘢𝘺𝘴 𝘵𝘢𝘬𝘪𝘯𝘨 𝘤𝘰𝘯𝘴𝘵𝘢𝘯𝘵 𝘤𝘢𝘳𝘦 𝘯𝘰𝘵 𝘵𝘰 𝘣𝘳𝘦𝘢𝘬 𝘴𝘰𝘮𝘦𝘵𝘩𝘪𝘯𝘨, 𝘵𝘰 𝘣𝘳𝘦𝘢𝘬 𝘴𝘰𝘮𝘦𝘰𝘯𝘦. 𝘕𝘦𝘷𝘦𝘳 𝘢𝘭𝘭𝘰𝘸𝘪𝘯𝘨 𝘮𝘺𝘴𝘦𝘭𝘧 𝘵𝘰 𝘭𝘰𝘴𝘦 𝘤𝘰𝘯𝘵𝘳𝘰𝘭, 𝘦𝘷𝘦𝘯 𝘧𝘰𝘳 𝘢 𝘮𝘰𝘮𝘦𝘯𝘵, 𝘰𝘳 𝘴𝘰𝘮𝘦𝘰𝘯𝘦 𝘤𝘰𝘶𝘭𝘥 𝘥𝘪𝘦."

Superman is meant to be busted because he's THE superhero. If Gunn is trying to go for that year one hero type thing, what he needs to do is actually read the comics, look at all the animated series and films, and then make the movie accurate to the character in a year one setting that way.

Superman has never been weak, and he's never had an issue knowing how strong he truly is. That is the issue fans have with this portrayal.