I don't know where this idea came from on the internet, that it's the professionals who are constantly chasing the latest and greatest. It's amateurs with too much money on their hands. Professional wildlife photographers have probably been locked into their respective systems (nikon/canon dslr) for years because you don't just replace your long tele glass easily.
When you look at some of the (very few) wildlife youtubers (Morten Hilmer comes to mind) they don't carry zoom lenses. They use primes because zoom lenses at that range have only ever been consumer grade. It's the same thing in mu43 too with the 300mm prime and the 100-400 zoom which is nowhere near the same quality. If the 150-400 f4.5 TC ever comes out that will be an actual Pro Telezoom for mu43 and something that really no other system offers. The usual setup for a wildlife photographer seems to be one 600mm/800mm prime (because most of the time you'll be zoomed in all the way to the long end anyway) and then something like a 100-400mm zoom (for when stuff actually comes closer).
Cropping from twice the resolution also gets you nowhere near mu43 reach. You would need four times the resolution for that.
Personally I find that the kind of shots that become accessible only because we can carry smaller gear anywhere is much more important than some marginal image quality gains that only become apparent when pixel peeping. You can easily print 40x60cm from the 20mp mu43 sensor. Tell me, when is the last time you printed larger?