That is broadly my experience with pure Ruby, yes. In terms of C extensions, I know they were doing some work on this but it was a WIP last time I looked, although maybe I should refresh my knowledge on this if it's now all good to go!
To give one example, DB adapters work just fine.
Since I have you, if you could humor me at all, what do you think the biggest current sticking point to average Rubyists just flat out switching to TruffleRuby is nowadays? Or isn't there one?