IF Ha-Shem wanted Hebrew to be pronounced a certain way, there would have been a sound recording at Sinai. Also in the above discussions, note that most Ashkenzim routinely mispronounce א, ע and ה. Indeed if Ha-Shem wanted Lashon Kodesh to be constant and unchanging, we would have been required to use a different language on a daily basis, since living languages constantly change over time.
Have you noticed than in English the gutteral “gh” which is “correctly” pronounced like a hes (ח) is almost always mispronounced (note that in words of German origin it is sometimes written “ch”, but also mispronounced. Have you noticed that virtually no English-speaker can read books written in English from the time of Rashi, and it is difficult to read English books from the period of the early Achronim without special training, and that native English speakers from different countries have trouble understanding each other (imagine some who grew up speaking Brooklynese trying to talk to someone from the Australian outback, or even from the American south – though English dialects have been reuniting since the inventions of new mass media in the 20th century).
So stop worry, and say Baruch ha-Shem that Lashon Kodesh is a living language, richly able to absorb new words, and never suffered the fate of Etruscan or Minoan Linear A (languages which never get butchered).