Hm, I hadn't really noticed the uneven gaps until now. So much for my attention to detail! I've added another photo to the listing that may or may not be a bit better than the previous ones.
I recall the stock keycaps being as expected, so maybe the issue lies with DSA R2, user error (me), or both. Although, to be honest, typing with them feels just fine, so I think I did a decent job of putting the caps on.
Now I need to look more carefully at my Code keyboard with Granite R1 on it to see if there are uneven gaps.