You are both completely overlooking two facts: first, Alexandria was home to faithful Christians as well as to false brothers, just as Antioch was; and second, the spread of Islam resulted in a great many churches being destroyed and with them, their contents. If a group of believers feared for the safety of their valuables, they could well have hidden them. Lack of use is not the only plausible reason for their survival.
In one sentence you claim, "no one can really pin down what Gnosticism teaches for gaining secret knowledge" and in the next you claim that prayer in the power of the Holy Spirit is about secret knowledge. Care to justify your massive leap of logic here? People who pray in tongues don't generally claim any secret knowledge by it, nor do they seek by illicit means to teach anything they've learned through such practice. I would strongly suggest that you do some homework on what the Gnostics did believe. Praying in tongues has nothing to do with it.
"I can only assume since no one can really pin down what Gnosticism teaches for gaining secret knowledge."
Then I expressed my assumption of relating this diatribe of self edification by tongues of today as mayhap referring to how the gnostics were gaining this "secret knowledge". It makes sense to me since Paul said in 2 Thessalonians 2nd chapter that this iniquity was already at work in his day of seeking that vain & profane babbling by receiving the Holy Spirit apart from salvation. The apostle John warned of it in 1 John 4:1-6 as the world does have a supernatural tongue by the spirit of error as this is gained by any one thinking they are receiving the Holy Spirit again for why John reminds them that He was already in them by citing "greater is he that is in you than he that is in the world" ~ 1 John 4:4
Paul's reproof towards that iniquity at work in his day can be found in 2 Thessalonians 2:13-15 where he reminds believers when they had received the sanctification of the Spirit & the belief of the truth at the calling of the gospel.
So let me put it in this way; the way tongue speakers are talking today of using tongues without interpretation for self edification, it sure does lines up with the gnostics' penchant for secret knowledge, would it not? I mean really. Think about it. How can knowledge be secret unless it is unknowable and thus not understood, but hey... self edification by tongues without interpretation sure fits the bill. I remind you it is my speculation since no one really understands what the gnostics are talking about as far as secret knowledge and why prayer, fasting, meditation, and doing good works was the norm rather than reading His words.
So yes.. that same prayer in tongues is the same one that believers claim today you can use for self edification, and why those at the Toronto's Blessing claimed that they do not need the word of God any more; all they need is the Spirit. If that is not what they had actually meant, it sure sounds like it... and goes to that possible mentality of the gnostics back in the day.
As far as addressing facts; how is it that you are ignoring what John 16:13 says in ALL BIBLES to see that all modern Bibles has it wrong in Romans 8:26-27 whereas the KJV has it right?