Nah Dude Season 1 was very well built. Every episode, even the first half had something that contributed to the plot or at the very least, world building.
For plot, I mean true it didnt ramp up that much until Toffee was actually introduced. But for that we needed to see many examples of how incompetent Ludo was as a leader.
For World Building, they dropped subtle hints as to the social structure of Mewni when it comes to monsters and such, and even just the royalty in general. A lot of it came together in Mewnipendance day, but there is still a lot to be seen about it I feel.
There was of course something new learned about characters in every episode too. And there was some build up to the Starco ship up to Blood Moon Ball as well, though subtle.
I'll have to look at my notes to see if there were any genuine usless episodes.