This is a non-argument. There are no spelling system in the world that takes into account every variation in the spoken language. Heck, even the current English spelling is based on the specific pronunciation of some part of England a few hundred years ago.

What all spelling system do, is just pick one dialect as the reference dialect, and build the spelling based on that. Is it perfect? No. Does it work? Yes, if the dialect that you pick is the most widely spoken and the most prestigious.