> If people like me, in perpetual MST, struggle to determine what offset is meant by "EST" then it's imprecise and misleading. We cannot merely say it's "descriptivist" and roll with it.

We can though. Say EST out loud like it's a single word. It sounds like "east," as in "eastern." Next, pronounce all three letters: E S T. It still sounds like "east." This is why people use EST when they mean eastern. They aren't talking about daylight or standard time, they're talking about the time in New York.