I do not know the etymology of John , but perhaps it's etymology in english actually comes from the "incorectly-made-up name "Jehovah". The anglification of the biblical names has always appeared very odd to me. E.g. He who in english is called John is in greek (which is the original language of the new testament) spelt "ioannes" and the apostel who in English is called James is in greek spelt "iakobos". I am not sure why, but perhaps it has something to do with why the etymology of John is Jehovah rather than Yahweh.
But one thing I do know. The way Yahweh is vokalized makes it impossible to pronounce "correctly". The name Yahweh consists in hebrew of the consonant: yod, he, waw, he. Those who later vokalized the consonants double vokalized the waw with both the vowel "a" and the vowel "o". Pronouncing the name correctly would then demand that two vowels were spoken at the same time, which is not possible. In the middelages they tried to solve that problem by separating the two vowels, which together with a few more rules of hebrew grammer, gave them the spelling Iehovah. (remember Indiana Jones III? Jehovah is in latin spelt with an I)
This attempt was later rejected and instead the problem with the double vowels was sought solved by simply ignoring the "o". Which made it possible to end up with the Yahweh pronouncation.
So neither Jehovah nor Yahweh are really the "right" pronounciation of Gods name. It is really unspeakable.
The Jews thinking that any attempt to speak Gods name is tabu use the "a" and "o" to vokalize Gods name in a way so it becomes Adonai meaning Lord. Thus they use the letters of his name but speak it not. Clever indeed.
This account is of course a little rough and I have left many details out. Still I think one should have a fair chance of getting an idea of the problem the attemts to solve it through time.