Honestly i dont have any rtx3000 or rx6000 series card because they expensive. I planned for the future.
An example -> RX5700 has 448GB bandwidth and do up to 55mh with oc -> RX6800 has 512GB bandwidth and do around 65mh if i am right. It is simple math. RX570 with 256 bandwidth do around 31 - 33mh.
Nvidia 3060ti and 3070 have the same bandwidth - so they have nearly the same hashrate -> a little bit more for the 3070 because more shader cluster (more shader makes give only a little bit more hashrate)
But you cannot compare bandwidth only if you compare nvidia vs amd.