This is wrong and I couldn't find a serious source stating anything like it. There's nothing in the Muslim faith that suggests the Arabic language itself is holy or sent by God.
The whole post reads a bit like a rant against Arabs suggesting their background precludes adaptation or something of the sorts.
I think what you mean is that they believe the Quran itself is literary perfection and sent by God through the last prophet, and that is indeed the belief.
But Arabs neither speak nor write like the Quran, and to the best of my knowledge they are well aware that their written and spoken languages have evolved through the centuries (as evidenced by the many Arabic dialects).
However, as mentioned most Arabs also believe that Quranic Arabic is that perfection. As a result, you don’t need to “improve” Arabic, individual people need to learn more Quranic Arabic that’s all. You would frequently see religious figures speaking in Al-Fusha to sound closer to Quranic Arabic. Not quite speaking in the convoluted nonsensical way of the Quran, but close enough to trick people’s ear into it. K-12 education teaches “Arabic” classes to every kid where they learn the “proper” Arabic often using the Quran and poetry from around the same time as the Quran as the reading and study material.