The true “original language” was Hebrew; John couldn’t even speak Greek, and certainly couldn’t write it. Hebrew also uses uniform letters, but that isn’t as important as the fact that every early English translator left ‘fathers’ uncapitalized, and did capitalize Father, when it referred to Yehova.
What I mean by your theory goes back to when you first offered the verse out of context in support of addressing men as father in authority. Neither John, Stephen, nor Paul ever did that. It was always generational when they used the word.
The full rules of capitalization for English are complicated, and have also changed over time. To us, an 18th-century document uses initial capitals excessively. And you can throw all this into the air when it comes to languages like German, which have entirely different rules for capitalization, with different implications for meaning.
Therefore I would caution against reading too much into capitalization or lack thereof, by English Bible translators: your argument could be kaput in German.
And the consensus among biblical scholars is that all four canonical gospels were originally written in Greek. Where do you get the idea that John couldn't read or write Greek? This sort of statement makes me think you are getting your information from sources radically other than, and counter to, Catholic, Orthodox, and Protestant Scripture scholarship.
Who are your scholars? Can you link to a website?