I'm not a fan of the new demo either, but meh, it happens... I enjoyed the other demoes. I think some (most) of Asterian's were pretty bad too, but I like Asterian. I chalked it up to most synth voice producers not knowing how to write music for a bass, since there's really only one other synth voice that I know of that's a bass (Vocaloid Big Al), and he was always kind of niche (and also never really written for properly, in my opinion).
Listening to the raw samples, did they use the automatic tuning function? If so, their default vibrato is fast and shallow kind of like Natalie's. Sort of reminds me of Michael Jackson a little bit or maybe Lionel Richie, interesting.