This isn't even debatable, since an apostrophe is clearly absent from all Ys logos (except apparently on the sega cartridge), and it is clearly pronounced by the narrator in the opening sequence of the game (Turbo Duo/CD Version). So there's your proof if you run into a special kid who insists otherwise.
There's never been any debate or anything. Ys fans have known how to pronounce the title for over 20 years. Aside from the Turbo-CD version's voice, the SMS version attempts to describe how it's pronounced at the title screen.
If some non-Y's fans want to call it something else they have every right to do so. Since official releases have Ys spelled "Y's", they can spell it however they want too. Many series and main characters are pronounced differently by different people and there's nothing wrong with it. The PC Engine isn't strictly the "Peeshee Enjeen".
But even if someone wanted to be a pwnage nerd and try to trash people for mispronouncing the title of one of the cart versions... why
should they know how to pronounce an unusual word like Ys if they've only played carts from the series?
This is what the
real hero of Ys looks like-
But I don't think anyone's a noob for mistakenly believing that Adol Kristein has red hair or that he
isn't 100 pounds over weight.