1. What reviewers are showing you that difference and how large is the game set? Again HU did a 50 game sample where only 3 games had RT, and he included modern warfare twice for some reason and the 4080 was 1% faster in 1440p and 1% slower in 4k. That makes them basically the exact same performance tier. If you’re looking at game sets that feature primarily AMD favoring games then yes you’ll see a big difference but you can do the exact same with the 4080 and Nvidia favoring games. Under a large sample size they are equivalent and it’s a wash.
2. Increase sample size
3. 100 bucks for the same relative GPU in raster with better RT, DLSS, efficiency, VR support.

If you don’t value those features at 100 that is fine, complete personal preference. But the 4080 is not a slower GPU. It can be slower for your specific use case but not slower overall. VRAM could be a selling point for you. I think 16GB is fine for the foreseeable future but if you believe 24 is needed then that is fine. It sounds like you’re sold on 7900xtx, I would just recommend getting one that is ideally 200 under and not overpaying for an expensive AIB