Someone comes up with a theory that's mathematically simple, beautiful, and consistent. That's great, but we don't consider it "correct" until it actually predicts something novel and we verify the prediction holds experimentally.
The core idea is plausible, if circular at present. That's OK. Now, we take that and run with it to expand on what we think we understand and hopefully, confirm and even more hopefully, crack open some new physics.
Seems like Einstein nailed it.
But, questions remain. Any of those could yield insights of similar potency and, ahem... gravity.
Someone comes up with a theory that's mathematically simple, beautiful, and consistent. That's great, but we don't consider it "correct" until it actually predicts something novel and we verify the prediction holds experimentally.
That's your "Y, therefore X".