Interesting that you use the idea that English is a living language to push back against people using a term in a way you’ve decided is incorrect. Seems like you don’t think English is that alive after all if you refuse to incorporate all Semitic people into the concept of antisemitism.
You can’t cite descriptivist arguments to defend your prescriptivist attitude towards the term antisemitism. It betrays your own bias and deflates your argument.
Language evolves, just like you said. Which is why people are realizing the double speak nature of this idea that antisemitism is only when you’re prejudiced against a specific Semitic people group and the others don’t get a term to describe prejudice against them. Your position is an Orwellian attempt to deny a group of people the ability to specifically identify their oppression and it’s sad.