Gosh, this is educational. I've always assumed (as a happy Olympus user) that m43 was mostly a photography format, and video people were all using Canons.
I've recently been hooking up my Olympus as a webcam, through tedious necessity - and of course it took a bit of adapting. I had no idea any mirrorless camera had a standard full-size HDMI port on it.
I know some Canon video people, and they definitely have a reason to do that at the "big" end (C100 and up): the Canon autofocus stuff is the real deal. But I don't shoot dynamic environments for video--I run video game events and mostly shoot static angles (players, commentary, the venue, etc.). In my realm--not film, but video--what I see on the high end are Sony A7's and Blackmagic Pocket Cinemas (the 4K is M43, the 6K is EF-mount), with a lot of LUMIXes and a few (very few) Canon mirrorlesses. Some people use Fujis they already own for photo stuff. Nikon does not exist.
The G9 and GH5 both have full-size HDMI (the GH4 does with the bottom adapter we all call "the Brick") and lemme tell you: it is a life-changer. Having to balance micro-HDMI (G7, GH4) and mini-HDMI (GH3) cables were bad enough and I look forward to adding more G9's to the kit so I can stop doing it entirely.
Video is a real rabbit hole, though, and not having to spend wild money on video cameras for completely acceptable quality has really helped me out. The way I typically run is that I go from the camera to a Blackmagic HDMI->SDI micro converter, but those top out at 1080p60--which is fine, currently, for stream-first stuff, but I'd like to move to "stream at 1080p, record for YouTube at 4K" as I turn my event production stuff into a real business--so I've added a Blackmagic Quad HDMI capture card that all of these cameras can just throw 4K60 at natively. Of course, SDI cables can run 100 feet and HDMI starts getting mad around 15, so there are baluns in my future, too...it's all weird.
I've recently been hooking up my Olympus as a webcam, through tedious necessity - and of course it took a bit of adapting. I had no idea any mirrorless camera had a standard full-size HDMI port on it.