I came from Canon and have been shooting sony for a couple of years now. The first iterations of the bodies had some pretty blatant deficiencies that even though I committed to transitioning, involved accepting some compromises...battery life, sluggish operations, no dual card slots, etc etc etc
With the a9, and a7riii, those compromises see for the most part gone, and the considerations to make are more subjective in nature (ergonomics, Evf etc).... But in terms of straight up performance, these mirrorless cameras are basically dslr caliber now.
In terms of why I fully transitioned...for me it came down to AF accuracy. I had been fed up with DSLR's and all its issues with microfocus accuracy when shooting fast aperture, and when I discovered mirrorless cameras do not have that issue, that benefit alone was enough for me to switch, even when the technology was immature and there were other compromises to be made. But again, now that mirrorless cameras are where they are, there is no reason for me to ever consider a DSLR. Eye-AF sealed the deal for me. Game changing feature for anyone who shoots portraits, and no that isn't hyperbole as it literally changed the way I shoot. I run a photography business shooting portraits, weddings, and events, and the system works fine.
YMMV of course. Depends on what you shoot.
Native glass tends to work better than adapted glass...and anecdotally speaking, most who pick up Sony as a second system and don't write it off right away, end up eventually fully transitioning to Sony lenses and getting rid of their Canon stuff. They do this because they like the upsides of Sony, and also because managing two systems is kind of a pain. That transition can be expensive, because Sony does not have the benefit of heaving 10 year old lenses that are significantly cheaper that stuff released in the past couple of years.
I'm actually pretty happy with adapted lenses for my uses, and even after having fully transitioned away from Canon, stepped backwards and picked up some EF glass again. Adapter performance is a moving target though. It improves leaps and bounds between bodies and firmware updates from the adapter manufacturers. Sigma released a new firmware yesterday that really improved the AF capabilities of Sigma glass. Most importantly, you will now track at 10fps. It's only a matter of time before metabones does the same via firmware, as they tend to mirror one another.
I'd pose your same question here if you want a balanced view. :
Most people outside of this thread are people who prefered to stay with Canon, as this is a very Canon centric forum. But this is a really active thread of Sony users made up of landscapers, portrait shooters, wedding shooters, sports and wildlife....most don't post outside the sony area, but yeah we all came from Canon: