I would say that my
speculation that Paul was talking about praying to himself and to God made up the majority of his "speaking in tongues more than them all," is based on the syntax of his sentence;
18I thank God that I speak in tongues more than all of you. 19But in the church I would rather speak five intelligible words to instruct others than ten thousand words in a tongue.
I think my speculation is stronger than yours that he always had an interpreter and never spoke in tongues
between himself and God. Why would he give instructions for them to do something he did not do?
28If there is no interpreter, the speaker should keep quiet in the church and speak to himself and to God.
When people interpret tongues today in the churches I attend the Holy Spirit does gives it to them.
Your opinion that it is only imagined, is an opinion.
As I mentioned a another post, many times I have received the interpretation because I was the leader and responsible to give it if no one else did, for mutual edification and then someone gave it and it was exactly what I was going to give. This builds great faith and demonstrates that we are not just making it up out of our imagination. The specifics of the interpretation made it impossible to be coincidence and this has happened many times.
I do hear in your explanation of what might have happened in the first century that you have a belief in the supernatural element of the gifts and I can imagine you would think that it was all a positive thing at that time. There is a certain building up of our faith and expectation when we read about it that God wants to use us today empowered by the Holy Spirit to reach a lost world. And I think when we agree on that we are all on the same page. Even if you don't agree with what you have witnessed through your past experience with Charismatic churches you seem to still be open to the idea of God using you in a supernatural way if He wanted to.
Many of us charismatics and non charismatics do agree on the concept of the "empowering of the Holy Spirit" to carry out the great commission. I even hear non charismatics talk like charismatics when they start preaching on the empowering of the Holy Spirit and you can tell that they are really open to God using them any way He so chooses. When we believe that God can use us today anyway He so chooses then we are less likely to judge others whom He is using in ways that we are not familiar with.
One of the reasons that I fellowship with Charismatic believers is because that is where I meet the most godly people. That is where I find the majority of sincere, Spirit Filled, holiness living, soul winners, who are living the best examples of what a Christian should be like. That has been my experience these 40 years and I can tell a HUGE difference when I get around non Charismatic believers. They are often indifferent and seem to be faking Christianity.
So we all have our testimonies about being around Pentecostals and Charismatics, some people have a negative report, but everyone I know has a positive report about them. Your testimony does not reveal "a problem" among them. It only reveals that you have a perception that there is a problem among them.