Hmmm, we use Yin release very frequently in the form of genjutsu, it's just that besides Hiden (which don't really have similar functions e.g. shadow possession, mind-body transfer) and actual genjutsu, Yin release doesn't have anything for me to work with and say
Yea, this sounds like a perfectly reasonable thing for Yin release to do!
To me, it's not a matter of it being too much, but rather you just have no real way to actually create a jutsu in practice.
Yin release just doesn't really have a consistent scaling for me to say whether it's potentially OP or not. Practically every variant of Yin release shown in the series is already present in the RP already, so I'm flat out at a loss for what you would even do with Yin release.
And beyond that, how would you distinguish it from Genjutsu? You could totally create flames and call it Yin release, but what's the difference between that and genjutsu flames?
It's simply an overall lack of a general mold to fit Yin release techniques into.
Edit:
and the Sharingan can already perform Yin-Yang release in its base form so ...meh?