> If it is known that A is provably true then one can study the consequences of A being true

But one can already study the consequences of P=NP right now. You don't need to know that it's provably true in order to do that.

Knowing an actual proof would be useful, but an oracle revealing merely that it's true (or even provable) without telling you the proof does not let you do anything you couldn't do before.

In this case won't this oracle also tell you what is the consequences as soon as it tells you RH is true and also much more? At this point what is the point of you knowing what is true and what is not?