But this argument (or this section of it) was about the practice of the early Church, and the Didache, etc. were adduced to address that argument.Exactly -- Those posts seem to want to say that someone 2000 years later knows more about the lives and practises of Early Christians than they (the Early Christians) themselves knew and wrote about!
If you want to say that it doesn't matter what the practice of the early church was, then it doesn't matter whether the Didache and Irenaeus were inspired or not.
If you want to say that the early Church went off the rails, then whatever the practices proved (or not) by the Didache and Ireneaus, they would be irrelevant.
If you want to say that you at almost 2000 years remove know more about what went on in the early Church than people far closer to it, then we have to assess the likelihood of that proposition.
But if all you want to do is to say that your way is right, and that's it, then what are we doing here?
Of course you know it's authentic?