I don't listen strictly to contemporary artists, the singers you mentioned do have phenominal range.
I have natural range, I'm just tightening it up where it needs improvement.
With modern R&B more and more vocal arangements and melodies/harmonies come with a more rapid delivery style.
Akin to an MC's flow as R&B had been heavily influenced by Hip-Hop in the 90's.
Keeping your range while using rapid delivery takes some work.