If she did exist, then she probably would get Hyper Voice. Most Dream special attackers get that as their main special Dream STAB, even if they're not a voice-related character; either that or they don't get STAB for Dream at all.
Well, other than Koishi anyway
Same thing with Binding Voice being used by special Beast attackers who'd have no reason to learn it otherwise.
And hey, what's so bad about vanilla Gengetsu? Steel moves/types are as obvious as Nature against TToyo, so you can use her on purpose to lure them out and pivot from there - she gets Reflect for that, too. And when something doesn't have Steel moves, she can work as a pretty damn fast bulky mon (if not the fastest mon with actual bulk any bigger than 80~100s).
Not that 80~100s aren't usable for some fast defensive mons, like vanilla Aya, but that's not the point.