If there was a license violation they should sue. Otherwise, writing a compatible reimplementation of something should not be something "open" fans are against.
I think OP's point is that AWS have the resources to reimplement all the differentiation you can try to add with an open core model like Redis tried, which makes the whole attempt at open core useless. Therefore the choice is either to try to partner with AWS like Grafana Labs managed to do (only ones I'm aware of), move to a license with restrictions on them reselling your code, or accept defeat.
Well even if they moved to a restricted license it would not stop reimplementations of the same protocol (I assume the extra non-open-core bits were already under a more restrictive license). I think that was just a poor example.