And Yet Physicists Claim Gravitation Is Weak In The Quantum Realm.

As you point out, this has never been empirically tested, but it is an article of faith among theoreticians. It is assumed that The Newtonian coupling constant G is an absolute constant at all scales.

If one is looking for a way out of the deep hole left by the glaring failures of supersymmetry, string theory, etc., then one might look to the assumption of absolute G as a possible cause for our paradigmatic malaise.