Do Not Play With His Name
One way we can be 100% certain that YA'OH is in fact the only correct pronunciation of the Creator's proper name is the way in which our ancient enemies once tried to mock it and then paid the price for doing so.
Take the Egyptians, for example. A popular legend that once circulated among the ancient heathens was that our people worshiped an ass. This damned lie originated among pagan Egyptians who passed it on to the Greeks. Here's the source of the information where you can look this up and not just take my word for it:
C. Stern, Greek and Latin Authors on Jews and Judaism, vol. 1, From Herodotus to Plutarch, 1976, I : 98.
Now, the Egyptian-Coptic word of "ass" is ειω. This is a two syllable word pronounced AY-O. The two letters ει (epsilon-iota) combined is the diphthong /ay/ (ει as in 'eight') and the letter ω (omega) is the long O-vowel.
In other words, the Egyptians knew the divine name of our Creator is two syllables pronounced YA'OH, and due to the popular play on words, they were able to mock it. This is why that country was destroyed and overrun by Arabs, Arabs who now treat the pyramids as public urinals, and loot the Egyptian tombs.
YA'OH was not amused. So He poured the Egyptians a tall glass of destruction and humiliation and He still making them drink it to this very day.
His name is YA'OH.
Always has been. Always will be.