Usually DeFi is a utility token or dApps which have some finance function.
So, it has to built on top of dApps platform like EOS, ETH, DOT, CLO, ADA or another platform that have capability for it.
By that fact, its impossible a DeFi replacing ETH.
There are many responses in this thread commenting on it even without knowing what they are talking about and you are the few that had a solid response that makes sense.
ETH and DeFi are entirely different things, ETH can be replaced by others like DOT, EOS or even BSC but not the other way around.