I understand that some of Mariah's studio material would be seen as 'emotionless' because they were very polished, i.e. Hero, but she made up for it with live performances. However, I think the criteria of 'emoting' is so diffuse that it basically just comes down to preference. I think that Mariah emotes really well on Butterfly, My All and I Still Believe, others might disagree.
In any event, I just don't like the misconception that great vocals immediately equals emotionless music. Like
Celine Dion would be my first guess though. Whitney is kinda hit or miss for me. I feel like a lot of their ballady album tracks are more about vocal dynamics than anything (All The Man That I Need for instance).
I might subconsciously be giving Mariah the upper hand because I know she writes her own songs. The lyrics she sings actually come from her, making everything more believable. Like if you know Mariah's story, one would probably have a better understanding for what songs like Butterfly and Outside are actually about.