I believe that ETH will reclaim it's glory back once gas fee issue is solved, there is also a big difference between BSC and ETH that will still make many prefers ETH, that's the fact that BSC is Centralized and ETH isn't.
I agree with what you are saying, ETH is a big platform that will not be easily replaced, the switch to BSC is just an alternative, no one really throws it away, everyone is still waiting for ETH to solve the cost problem.