I've contemplated the thought of dropping Canon for Sony on more occasions necessary ( weight / size ) and have yet to take to plunge. I have a a6000 i toy with here/there and enjoy very much, but I'm so heavily invested in Canon that I feel I'd be losing more than I want at this time. Even keeping my lenses and just dumping the bodies, I have yet to see/read anyone who use ONLY adapted lenses on their Sony Body to help with my decision making.
Most of us transition to native glass eventually. Partly because a lot of the native glass is really good, but partly because adapted AF involves compromises. I'd say with the a7rIII, unless you're shooting really long focal lengths or need fast FPS, there's less need to use native glass these days.