I will say it's a tie between Dinah and Ally being the top two vocalist in the group. People are only judging their vocal ability based off certain songs. The third best vocalist is Camila, But always try to come for her being extra and her tone being grating, but she's way more consistent live than Lauren. Even Normani is more consistent than Lauren live. Lauren has a nice tone, but she's not the best vocalist in the group, when she's the least consistent live.
Yes, Dinah is the best vocalist, but she's been having trouble lately. Her breath control is terrible. She still has the best range and vocal power though.
I'd say the rest is pretty much equal. Ally has even worst breathing problems, Lauren is not consistent at all and 90% her voice is way too raspy, Camila can be nasal and Normani has improved a lot but, to me, she's still the weakest.