Well to be frank, I think Yuu is the only one lacking (not for her seiyuu's lack of talent of course) as she just sounds too soft and meek. A deeper voice really would have helped there. But that is not really a fair assessment.
Hey, I just want to point out my agreement with this point (not that i dont agree with your other point ofc).
I also feel sometimes Yuu's voice is a little bit too chirpy. she's more of a calm and collected kind of character, sometimes even seemed a little bit distant, like a lot of characters point out. In the anime there are moments where her voice is a little bit too high, it kinda bothers me
But if I have to pick, I think the seiyuu nailed Yuu's voice on the first part of the 2nd episode, where she complains about being selected as the campaign representative to Koyomi and Akari. And just like you said, in that part, the seiyuu actually sounds deeper. And also the 'unfair' moment. I hope we see a lot of this Yuu moment in the future
But again maybe it's because our perception as a reader influence our cognition of the anime. Regardless, i really enjoy the anime, it's one of a few adaptation that i love bcs it's faithful to the manga