By the same arc do you mean a character overcoming an emotionally difficult moment in their life? While that's true, it's also true for hundreds of other stories.
Of course it uses the same premise, that's the point of this story being told as an "inside out" film.
I feel that it should be judged on how well it can help the audience emphasize with the characters (not the emotion characters, but the human girl) and the trials that they are going through while also being entertaining, educational, or thought-provoking. In this regard I think it did a pretty good job of showing how tough puberty can be. As a parent of a kid about to hit puberty, I think it did an excellent job of discussing these issues.
The "inside" part was the same story, the "out" part was the progression of Riley growing up. Riley's circumstances forced some emotional growth and the internal narrative depicting that growth had the same story as the original film. The internal struggle apes the original beat for beat.
It sounds like you resonated with the external struggle, that part was great, but I felt the internal narrative didn't carry its weight this time.
I feel like the outside story was much more important in this one. In the last one, Riley's story was much less emphasized. It dealt more with how emotions impact the outside world. I think two dealt more with how each one impacts the other.
I do agree that the inside story didn't quite have the originality it could have, but I also think it'd be very hard to tell a story in-universe while changing the Inside mechanics enough to be a more unique story. At the end of the day, you're going to need balance. That's not going to change.