After watching around 10 episodes of the new season, I'm finally understanding my problem with it.
It's moralfagging. Most episodes try to end on a positive note or with some kind of lesson. I don't inherently mind this, S1 of TAWOG had some of it, but the show was a lot more measured then. Now the humour is out there so when they reign it all in in the final few minutes it just feels hollow to me and a bit like a waste. I prefer the endings that are more cynical, because Gumball has typically been a bit more of a cynical show. Too much redemption.
An example would be Molly. In TAWOG she's a joke every time, in the current season she gets her own back at the end because it's "wrong" of her to be treated like that. Many things like that where it means gags aren't landing as hard and the endings of episodes I'm just waiting for a soppy feelgood ending that Gumball itself used to kinda mock.

That's my take anyway. I like the show, but the new season has felt off and even episodes I've enjoyed felt far from peak