I remember people were expecting Hulk to be Godly. To me, it sounds like it was perfect. This is Thor's world, not Hulks, not Tony's, not the US army. This is Thor's world of gods, monsters and mythology.
In this movie, Hulk literally encounters the 4 most powerful characters he's ever met. If they are drawing from mythology and simmonsons comics, yeah, from an objective feat/mythos story telling standpoint, Fenris shouldn't be easy work for Hulk and should be too much for him, as should an all out Thor, Hela, Fenris, and Surtur. He shouldnt be able to beat up a character to is historically above him, simply because "he's Hulk, and forget continuity"
Doesn't sound like Hulk was nerfed, or "should have been more powerful" here, it just sounds like the writers didn't boost him up and lower the other characters..his powers were scaled accurately as the should be.
People are conditioned to Hulk being overall "strongest one there is".. not in Thor's world with him, Hela, Fenris and Surtur. With characters like that Hulk SHOULDN'T stand out. He is a heavy weight playing steriod heavy weights and peak humans