I can’t say I especially like this reasoning. I don’t think that whether a villain has or doesn’t have sympathetic motives for what they do is a determining factor in whether they’re a good villain – it’s entirely possible for a villain with unknown motives or who is motivated entirely by selfishness, lust for power or cruelty to be a compelling character and antagonist. A villain is made interesting by how they’re written, how they interact with other characters and how their motives and aims, whatever they may be, are used to reinforce the story’s narrative and morals.
@PawelS
None that I can think of. As far as I know, she was motivated chiefly by self-entitlement. She wanted power because she felt entitled to rule, by and large.
@PonyPon
How? Celestia ended up at odds with Sunset in the first place because Sunset was selfish and obsessed with being an alicorn. Sunset’s troubles were entirely of her own causing.