I suppose it depends on the folks you know. In my world it is much closer to 50/50, with many folks using elements of both.
'Your world' is full timers though, right?
There are not many of them compared to all those graphic designers who do type design but aren't focused on type design full time. The austere (dutch? culture of RoboFont isn't a good product-market fit for them, because even if you don't write any extensions yourself, it just takes too long to get up to speed with Mechanic and adding all the features you want one by one. I think for full timers you are right, taking time to learn RF and having both makes a lot of sense.
But if you're not, Glyphs has a 'just works' and 'batteries included' approach - so its much more popular.