The same is NOT true for dexamethasone, well not exactly, since there was no directly competing drug. Dexamethasone, which you can probably confirm, is useful in the later stages of COVID where there's an inflammatory response. Since no other proposed medications were seeking an EUA as a "late stage" therapeutic, there's no chance the already approved Dexamethasone would have blocked the issuance of an EUA.

That's at least my understanding based on the proposed systemic problem in FDAs.

Conversely, in this proposed problem, it's said that ivermectin (and others) are only effective when used in the early stage or even prophylactic. Being already fully licensed medications, that could put the issuance of an EUA for vaccines or Remdesivir in jeopardy.