jassey,
I upgraded from a T7 to a 90D ath the end of last year. I think the T6 and T7 are pretty similar cameras except for the the sensors (18mp vs. 24mp) and maybe the lens mount (plastic vs. metal). Other than its similarities to the 90D, I'm not familiar with the 80D. But because of those similarities, upgrading from a T6 to either the 80D or 90D will be a significant step up and there will be a lot to learn.
Here's my thoughts regarding upgrading to a 90D:
1) As Rick said, going to an R50 or another mirrorless body is "future-proofing" your camera selection. It's another variable for you to consider.
2) The 90D body is larger, beefier, and heavier than the T6 or T7. I liked the compactness, weight and ergonomics of the T7. The 90D lacks that compactness but maintains much of the same familiar ergonomics adding additional features, ugrades and heft of a serious pro-sumer camera body.
2) The focusing system on the 90D is remarkable. I expected much faster focusing but the focusing speed and accuracy and the multiple combination of focusing modes and options of the 90D is almost mind-numbing. There is learning curve to knowing which combination of Focus Area Selection to use and when, but once you start to figure that out, its hard to miss focus. Additionally, if you shoot in Live View using the back screen, the 90D is essentially a mirrorless camera.
3) The 32.5mp sensor in the 90D is a "monster". I'm surprised how much I can crop in and still maintain detail and the high ISO performance is remarkable. I percieve that there is a difference in overall sharpness and detail in my 90D shots compared to the T7's 24mp sensor.
3) With the the 90D you can shoot at 10fps (11fps in live view) vs. 3fps on the T6.
4) You didn't mention which lenses you own and use, but with the 90D, some lenses will work better and some older EF lenses that were introduced in the 1990's for EOS film cameras will not work as well. I found that my EF-S lenses work better on the 90D than they did on the T7. They focus faster and more accurately and with more focusing flexibility/options as described in #2 above.
5) Although EF and EF-S lenses are no longer produced, there are probably millions of them out there and lots of places to buy used EF and EF-S glass. I don't have a crystal ball, but I'd think that those of us that use EF and EF-S lenses shouldn't have much of a problem finding good used or reconditioned lenses for the next 10 years or probably longer and hopefully at decent prices. By that time, many of us will have upgraded to mirrorless anyway.
I hope the above helps.
Regards,
LZ
