Lol at comparing demonstrable advanced technology like quantum computing to phlogiston.

Anyway, experiments to prove/disprove phlogiston lead directly to our understanding of combustion and discovery of oxygen...

I think you rather miss the point, when electricity was postulated, no-one would know where it would lead, I point out that the same is true for phlogiston; one changed the world and the other went nowhere. My point is that just because something has so-far not been shown to be useful does not imply that it will eventually change the world.