The A7RII has a great sensor and some still prefer it or the same sensored A7RIII over the later 61mp A7R4 / R4a / R5.
It also had the smaller NP-FW50 battery and all following bodies got the bigger NP-FZ100.
It's AF was also improved greatly with the A7RIII. Not only with native lenses, but adapting went from just useable to quite good in many, but not all cases.
The cheaper 'non R' line also improved significantly, the A74 is 33mp and AF greatly improved.
So for your use, the A7RII will continue to achieve excellent results for as long as it works.
Any upgrade in the future (to later Sony body) will provide much improved experience but not necessarily big difference in IQ.
While I never looked into the newer editions, you are spot on in that I realized its capabilities and am still learning all it has to offer. The images, IMO, are more than crisp and sharp, and the camera is a highly capable piece of gear. The learning curve was a bit of an obstacle being an avid Canon fan, but it really didn't take long to find my comfort zone with it and all it has to offer. I will keep it and enjoy it. The batteries are small, and when I purchased the body, I soon purchased additional batteries for that reason. I haven't look at any of the Canon R gear as I have no interest in changing up my current equipment. Money is always a consideration of course, but for what I shoot, I simply don't need all that the R series has to offer. Fortunately I am beyond the GAS (gear acquisition syndrome) and I'm happy with what I have!
The capabilities of the mirrorless are that compelling!

