You forget that, like as with Scripture and tradition, church history only means what Rome says it does, as Manning essentially argued in order to deal with contrary testimony:
t was the charge of the Reformers that the Catholic doctrines were not primitive, and their pretension was to revert to antiquity. But the appeal to antiquity is both a treason and a heresy. It is a treason because it rejects the Divine voice of the Church at this hour, and a heresy because it denies that voice to be Divine...The only Divine evidence to us of what was primitive is the witness and voice of the Church at this hour. Dr. Henry Edward Cardinal Manning, Lord Archbishop of Westminster, The Temporal Mission of the Holy Ghost: Or Reason and Revelation (New York: J.P. Kenedy & Sons, originally written 1865, reprinted with no date), pp. 227-228.
Indeed. It is a painful tautology. The whole phrase you quoted from the Cardinal boils down ultimately to, “We’re right because we’re right.”