I've used many systems; I started with 35mm film, then 6x6 film, then 4x5 film; loved all of them except 35mm film. Film real estate was king. Then came digital, Nikon D70 through Nikon D800e. I fell in love with Fuji, small light, high quality images but then...
I developed megapixel lust; not clear why because i never did huge prints, but the Sony A7RIII with its 42MP sensor seemed like heaven and I've not looked back.
I'm a bit of a dinosaur with modern tastes. I just got the A7RVI and it's quite a camera. It will do ANYTHING I might want, from striking landscapes, to intimate still lifes, to my busy grandchildren. I have total control over so many functions. Pixel peepers may imagine may differences, but for anything I do now or will ever do with a camera, the A7RVI is more than sufficient. I looked at the 100MP choices (really just Fuji and Hasselblad) and while they are superb machines, they are too expensive, too big, especially the lenses, and too slow to operate except in the landscape. Not for me, though I still drool when I see someone using one of these lovely cameras.
Don't get me started on lenses. Even though I realistically use only a few at any given time, the selection of OEM and third party lenses is unsurpassed. If you can't find an e mount lens to solve your photographic problems, you're either in a tiny niche or you're the one with the problem.
That's why I'm with and plan to stay with the Sony Alpha system.