Against a high-priority target, certainly. If this thing gets off the Z-Draco, and its opponent is not a Fairy, Chansey, Blissey, or a specially-defensive Steel, something dies. Period.I can't speak for lower tiers (although in theory, I think you are right), but my biggest concern is how much more damage is a Z-Dragon move doing compared to a LO Draco? And is avoiding the SpAtk drop (or other downsides potentially) and the one-time nuke worth losing the extra damage over the whole battle? I think its really hard to say without testing and getting an actual feel for it in-game.
It's a lot like the Gems from the Gen V metagame, except the Gem can't be knocked off and there's no risk of missing or stat drops.