The ignation letters with or without the controversy prove nothing more than that someone believed the things he said. It does not prove they are christian teachings, that the author was christian or that the teachings are in any way consistant with scripture as it exists. Nor does it prove that the people who believed those things were christians rather than the miscreant followers of false doctrines that were being warned of already at the time the NT was being written by people who were Christians and were consistent with one another though somehow not with whoever it is purporting to be ignatius in that letter or the others.
You see scholarship doesn't just look for a name and accept blindly what's attached to the name, it looks also at whether what it claims to be stands up in light of what is already known. In the case here the known is pre-existing scripture. It's like finding a letter purporting to be from einstein that says E=M^5 - C. And dated six days after his death. It shows someone had a passing enough knowledge of the subject to get some elements right; but screwed the pooch by getting half of it wrong. The half that's wrong voids the entire relevance of what was gotten right. The date, what's wrong and the end result are not important to some, though. The wrong half is what's strived after placing the face and the appearance of propriety above the truth in order to establish credibility for the junk. Ie the argument - Look, Ignatius wrote it real early and people believed this - and look, it looks like he's christian so this must mean christians believed this. So let's all just ignore everything else on the subject and interject everything he says without considering whether the content is worth the paper it's written on. And accept it on it's face as proof positive of someone's otherwise unsupported claims. See the consideration as to whether it supports you is a ways down the list. Before that comes things like, are the teachings in line with scripture, regardless of who wrote it or when.
Finally, let's underscore something even more disengenuous that comes from the translator. In english, that should say "universal church" not "catholic church". It is an adjective, not a noun. The fact that it is not fully translated out allows people to interject it and run off at the mouth that it's a noun as much as specifically changing the first letter to a cap. It's called intellectual dishonesty.