The term "Professional photographer" is someone who is making a living off of photography.
This is were there is no set policies or procedures in how to conduct his/her business.
A "Pro" can shoot with and iPhone or 10yrs+ dslr or even a point and shoot as long as they get paid. My point is the term "Pro" is used with no definitive benchmark or mandated rules.
I think "FEATURES" is something that should be emphasized as mirrored or mirrorless have different characteristics due to different technologies.
The Micro 4/3 world has evolved a lot but I really do feel it's at a point of hitting a wall in maxing out it's maximum potential at this moment in time. Physical size of sensor is the limiting factor. For a person shooting articles on low res print can easily use the latest M43 system but when low light situations happens it's far from ideal. Big thing at the moment is "inexpensive" long telephoto needs for people compared to $$$$$ Canon/Nikon/Sony telephoto lenses.
If weight isn't a factor a universal beast like the 1dx series, 5dmk4, Nikon D810/850 or lighter setup Sony A7iii (for the cheap), A9 can shoot from fast action, low light clean files, less AF hunt, thinner dof using zooms etc. As you can see this is a list of a mix of mirrorless and mirror.
Wait till Nikon and Canon produces "worthy" FF mirrorless and this topic will shift. A Nikon die hard will say I use my D850 (or whatever newest body avail) and my Z6/7 mk2,3,4 and have a heavy or light combo. Same goes for a Canon user waiting for EOS R mk2,3,4.
Canon and Nikon will eventually produce incredible FF mirrorless bodies..right now...NOT!!! :P