> Adapting the plan at runtime seems like the most universal solution for optimizer edge cases and is already implemented in the big 3

But the issues frequently aren't edge cases and frequently are at runtime (i.e. new query), it's just the best the optimizers can do with limited info (cardinality) and a limited duration to evaluate alternatives.

EDIT:

I just realized I misunderstood the post I responded to. I thought adapt meant update the query plan that was previously stored, but I believe the meaning is during execution of the query.