I'm... actually gonna have to disagree with this. I'm admittedly more of a Derpy/Ditzy fan than a pony fan in general (which is why I ended up watching the bit with her in the first place!), but... I found the scene with her p. problematic.

I'm actually glad to hear the VA was going for "sleepy-sounding boy," but it wasn't really JUST the voice, or just the eyes. It was a combination of her seemingly complete inability to understand what she was doing wrong/that she was breaking things, plus the way Rainbow Dash was treating her, plus the voice, plus the eyes. The combination of those things came off as coding her mentally disabled, with a side of "hey guys mentally disabled people are funny, it's okay to find any mistakes they make hilarious and then yell at them for it." Maybe an adult can look at that scene and follow your train of thought, but MLP:FiM is a show that is also aimed at kids, and not all of the kids watching the show are going to be mature enough to see more than a dumb, klutzy, slow-sounding pony being presented as comedic relief.

Maybe I'm being a bit serious about this, but both my younger brother and I have eye issues too, and while neither of us are quite that wall-eyed it kind of sucks to see a character with issues similar to my own being treated like that.