Man, that's what we all said when were were told to move from Blaze to React. Look how that turned out.
I just learned React/Redux (everyone was right, awesome frameworks!) and am now planning to migrate from Blaze.
That's what we said of Facebook, then MDG stopped supporting Blaze/Tracker and moved to a React + Apollo focus. And again, not to undercut your point too much, but Facebook just doubled down on both React and Relay with a complete rewrite -- there's no way they're standing still -- their "hundreds" (or thousands even?) of engineers won't let them.
I guess Blaze was before your time.
But you just said yourself you haven't even seen Relay Modern, how do you know for sure?
Also, I'm not here to promote Relay Modern over Apollo -- I don't know either tech yet (but these two are next on my list). They both look interesting and I think it's worth while to explore both options.