Rome’s ultimate political form - empire - was corrupt, brutal, and stagnant. Its collapse was a necessay precondition for the development of the European nation state, a far more dynamic and potent political form that, in its greatest incarnation as the United States, looked to Rome’s republican ideals and the stock of experience generated by Europe’s nation states. Rome’s history thus proved to be far more useful than a continuation of the Roman empire could ever have been.
As Christians I think it might be satisfying to think it was Rome’s cruelty that brought them down but somehow I doubt it.
Even a corrupt Roman Empire very likely would have proved a more stable bulwark against 1300 years or more of Islamic expansionism, it surely would have proved a more secure library of the wisdom and science of antiquity which, as you point out, our founders found instructive.
