Utilizing legacy characters just adds another layer to it.
It’s mostly a layer of controversial updates, fan service and audience hooks, though. Why not replace it with layered new characters?
Sorry, but except for TOS no Star Trek show has ever stood on it's own.
All your examples are merely rare, fun guest appearances in shows that do not normally reference one another. TNG almost never revisited TOS locations, DS9 couldn’t care less what Picard was doing or where Voyager might‘ve been at a particular point in time. Berman didn’t allow it, or we would’ve had things like the Enterprise-E featuring in the Dominion War or Barclay constantly looking for Voyager from the Gamma Quadrant.