Muman, this is not an issue of "Sephardi vs. Ashkenazi, who's better" or "who's more accurate" .... Nobody is discrediting the Jewish mesorah (as a whole) of Ashkenazim or questioning the backgrounds or Jewish ancestry of any of these groups.
The fact remains, that the pronunciation of Hebrew by BOTH of these groups has it's problems. Notice, Sephardi Panther cited the TEYMANIM - These are the Yemenite Jews - who maintained a tradition of pronunciation unique from BOTH of the current Ashkenaz and Sephardi pronunciation, although in more ways similar to Sephardic. The bottom line is what is the correct way to speak our holy language. Not who is right or wrong or who is the best or closest. The point is, since the Hebrew language is the holy tongue and so important as it was crafted, let's try to adhere to its actual guidelines, be the masters of our own national language, and pronounce it properly as God intended.
Errors and mistakes crept into the mesorah for pronunciation by different groups in different areas, and this was a natural historical process, when people ended up in places where the common language had sounds that were different from Hebrew or didn't contain some of the unique sounds of Hebrew. This is why Ashkenazic Jews only pronounced waw as an undotted Bet, a bh or V sound, because in Ashkenaz and Europe they did not produce this sound W in the local languages, for x amount of time, enough that it passed out from the spoken dialect of the Jews in their prayers, etc. There is nothing wrong with acknowledging these mistakes and adjusting accordingly, and the work of linguists and grammaticists elucidates the proper Hebrew format. Chief among them is the great Grammarian and one of the greatest, most learned rabbis of all time, the Saadiah Gaon. He gave us explicit instructions and explanations regarding pronunciation that other later sources did not necessarily take time to explain. And given the early era he lived in, he can be relied upon for the bulk of this linguistic analysis.