Perhaps a more gradual influx of barbarians on the borderlands could result in a more Byzantine decline, where the West is slowly reduced to Italy? Invasions and coups would probably still lead to its fracturing like OTL, but this development might take centuries. Conflicts with the Pope would still be an enormous issue and alternate forms of Christianity, or autocephalous churches, might predominate as Roman Catholicism would be associated with Imperial authority. This would result in an entirely different Middle Ages. Might be worth a TL.