yah, both can be repaired to be visually seamless, but plaster can be functionally seamless too. mold seems to love drywall but can at least be scrubbed off plaster. i've done this with bleach, which apparently some mold is resistent to, and then topped it with mold-resistent paint (since it was under/behind sinks/vanities, i didn't really care if the color matching wasn't perfect).
when i was researching how to repair plaster, i learned that old-school plasterers used to make 3 passes to make it perfectly smooth on top while thick and sturdy throughout, starting with a rough "brown" layer for the bulk to a fine white layer for aesthetics and water resistance. it takes skill to do but the results are both visually pleasing and resilient (having lasted ~100 years so far in my building).