Even so, it is certainly possible – even likely – that separate groups of early Christians had their own peculiar customs, jargon, and “style,” just as the various religious orders and other groups within the Church have today. That does not have to mean that John’s followers were not orthodox in their beliefs, or not Catholic in the broad sense, even if they might have emphasized different aspects of the Faith than, say, those who had learned from Peter and Paul in Rome.
The main thing I find objectionable about the common use of the “Johannine community” in discussions of Scripture is the seeming assumption that they were, at best, distantly connected to the original John when they wrote/edited/completed the books assigned his name in the New Testament. As others have pointed out, tradition has Joun living until nearly the turn of the second century. Ignatius of Antioch wrote not long after and was an elderly man when he did so – there are stories suggesting he was one of the children who flocked around Jesus in the Gospels, and even if not, he was in the right age range. Even Irenaeus, who wrote at tail end of the second century (by which the NT books were complete even according to the latest of the proposed dates), knew Polycarp who’d known John. The notion that the New Testament was written (or at least finished) by people “generations removed” from the Apostles might technically be true, but the accompanying implication that those people weren’t really carrying on what Jesus and the Apostles taught in their lifetimes seems to ignore that it’s quite possible to have personal contact with someone one, two, or even three generations older.