You'd better tell the WR Dictionary then. It gives:
most favorable or desirable; best. Collins and the OED agree.
Mind you, optimal is often used when we mean "best
in the given circumstances", so there can indeed be several optima. But that's no different from best: "These boots are best in wet weather and those sandals are best in summer: each is best in given circumstances." "But which is the
most best?"
Replace
best with
optimal and nothing has changed. You can't say
most optimal.