Meta/balance has very little impact on overall popularity of a class/spec, even in Mythic raids. Only at the real top end (Hall of Fame/M+ title) does this really break.
https://www.dataforazeroth.com/stats/classes/level70 -- This data isn't perfect but I can't imagine it's too far off. I know the top 3 are almost surely locked in.
Even just looking at # of parses/kills by a class/spec on WCL, some specs are always over/underrepresented compared to their strength because they're just more popular.
imo Tinkers would need to be available to non-goblin/gnome races to get real popularity.