bnb is commerical stuff but eth is public tech stuff. if we talk about price, once a day bnb burn %70 of circulated token it should overtake.
Yes you're right, BNB is just circulating and trading in binance which for binance commercial and it won't replace ETH in a side of usage and function.
But if the question is, will BNB marketcap will surpass ETH , it could be just happen
and this coin can only be use in there palform no real use cases in other thing unlike ETH .