I’m not saying the performance is acceptable, I’m saying your comparison and expectations relative to your 4k performance was flawed in a couple of key ways and have explained those at length already.
However I would suggest you have some opportunity to improve things because I can run at a solid 30fps with mostly medium/low on a 3070 at 70% resolution on a G2 which is significantly higher resolution than the index (at 100% it is trying to do over 3k x 3k per eye!) take a look at this thread for some settings optimisation advice which will also help with your 3080 (you’ll just have more headroom to turn things up higher or to shoot for 45fps).