Another feature of a dispenser that is still the case presently [1.16 and later] is they are also able to place shulker boxes. And shulker boxes can be filled and emptied in the same way that chests can be with a hopper/dropper system. So while it doesn't help with Ore placement unfortunately, you could technically clear out one level of the Y axis and replace it with obsidian. Then set a minecart < hoppercart system underneath the obsidian.
Then, dispense lit TNT into the area destroying everything above your obsidian level, and leaving behind whatever to be collected in your minecart < hoppercart system, sorted through hopper/ dropper/ water systems and with dispensers able to place shulker boxes, you could fill the shulkers until full, then break them down with more TNT and water, or pistons. End result being shulk-full of all ore and rock types not completely decimated by the tnt to begin with. =]
Theoretically, of course.