I would only agree up to a point. Certainly the Celtic Church saw itself as owing loyalty to and in communion with Rome. And no doubt the degree of separateness has been somewhat exaggerated by historians of either a protestant or chauvinistic bent. But such evidence as we have suggests that Rome regarded the pre conquest Irish church with at least a degree of suspicion in terms of its practice and doctrine. It may have been the only English pope who authorised the English conquest but his decision was quite uncontroversial in Rome.
Lots of popes have raked lots of local Churches over the coals because of perceived doctrinal or practical irregularities, but that doesn't mean that they were considered separate Churches. E.g., Leo I was so concerned about the praxis of the Sicilian Church that he made them send delegates annually so he could tell them if they were doing anything wrong, but nobody talks about "Sicilian Christianity" as a separate Church to Catholic Christianity.
And of course, even if Rome was suspicious of the Irish Church by the 12th century, there's no evidence of such suspicions in earlier periods. So, any claim that the Irish had practised a unique form of Christianity from the time of St. Patrick seems dubious.