Look, the Church understood it from the beginning to mean triple immersion and for a good reason. The language of the Church was Greek. This is not some private interpretation or a matter of private taste. If the immersion is misunderstood Chrsitians outrside the Church, you can imagine what else is. Making a church according to one's private preference is a man-made "church."
You’re right, matters regarding salvation should never be a matter of private taste. Yet as you noted yourself, the interpretation of a triple immersion is without scriptural support, and is/was a matter of private interpretation.
Whether this interpretation is recent, or ancient is not the question.
If a triple immersion was vitally important, would not Christ and his Apostles have CLEARLY spelled it out? The fact that they used a word that has implications of multiple immersion does not mean that it is automatically so (much less 3), and as Greek speakers they would have been aware of this possible interpretation. Yet, being aware of it, they did not see the need to stress that it was triple.
You place a lot of stress on not interpreting the scriptures according to personal taste, and this is entirely important. Yet merely because an interpretation was made centuries ago does not exclude it from this necessity. The highest authority we have is scripture, guided by the Spirit of God, and it is to this that we must constantly return.