It’s why I want to see a 1.5 stop improvement. That will have to hold up for 3 years in any particular camera model, even though companies will have even more updated sensors in cameras they release a year or two after that one. Just remember that Nikon/Sony aren’t standing still. What may slightly beat them this year, may be noticeably behind them in a year, or two. So you want to stay ahead of that now.
I hear you, but that's neither reasonable nor consistent with the trends of sensor progress over time. Using the generically cruddy numbers from DXO (as a convenience to make a general point):
A7 I: 14.2 Base ISO DR / 2248 ISO (using their SNR / DR / Color high ISO cutoff)
A7 II: 13.6 / 2449
A7 III: 14.7 / 3730
A7R I: 14.1 / 2746
A7R II: 13.9 / 3434 (in fairness, this is a jump from 36 to 42 MP here)
A7R III: 14.7 / 3523
From gen I to gen III, both A7 lines above gained a fraction of a stop of DR and high ISO performance. A fraction of a stop.
It's easy to look at how these sensors test (or how RAW files handle in post) and declare the latest product 'the best ever' -- but when you look at it critically, it's more a trend of creeping up on an asymptote over time.
O course, on chip ADC was a huge deal. But everyone's done that now and any one-time bump to base ISO DR is effectively industry standard now.
Yes, Canon sensors are behind Nikon and Sony. But they are not tremendously behind them for me to want to walk away from the EF lenses + first party AF routines, build quality, ergonomics, service, 3rd party ecosystem, etc.