I'm no music expert and this is all my own totally amateur opinion, but I think a good and recent example is actually Calli vs Mumei singing Stellar Stellar:
I think Mumei is a better singer than Mori and her version sounds good, but I actually like Mori's karaoke version here better because she sings it with the same level of emotion Suisei would because she understands the lyrics and their meaning. It is definitely not a skill difference between the two, as well, because Mumei can sing
incredibly well and emotionally.
Idk, though, I am not particularly musically inclined, though. It is just my autistic opinion.