I just want to chime in with my short experience with Content ID.
Last year I registered half of my tracks in Content ID, the more unique ones mainly, those that I feel more “personally attached” to. Months went by and saw that my Content ID tracks were actually selling the best, could be coincidence of course (or maybe just because they are more interesting), but I decided to register more of my tracks just for the reason that my more steady sellers were registered.
The last half a year or so I have been receiving merely cents in AdRev (the content ID provider), based on 2-4 registered video uses a month ish. BUT the last registered month suddenly I had jump to 60 + videos registered earning me around $16. Still not much but definitely promising development in a revenue stream I have had very low expectations, and especially fun to get links and see where my music have been used, and yes obviously a lot illegally, quite a few gaming videos.
But since every Content ID track is plastering my author name and track name in the illegal use description + giving at least some kind of revenue based on the views I see this as great promotion. I do not know where they have gotten my music from. I have been spreading my music around to several sites the latest months but I also started uploading a track to Youtube every week a couple of months ago. I have very little subscribers/views so far, so it seems weird that these people found my tracks at my Youtube channel, but who knows.
Anyway, I definitely see the challenge with content ID that some buyers (and stock sites) get anxious about the clearing process. Hopefully in the future this process can be a more streamlined effortless thing, which it should be.