I do not believe there is a trend of calling "everyone you can't stand a [something]-supremacist" -- surely this is a dishonest retort to a label that is being applied very specifically to a radical nationalist.

Now, if your dispute is that you think there's daylight between an ethno-religious nationalist and an ethno-religious supremacist, fine, make that argument, but let's not act like the label is coming entirely out of left field. And please be aware that if you draw a distinction between those things, you provide cover for actual [something]-supremacists, because god knows David Duke has had no problem saying "gee whiz, I'm just saying I see America as a homeland for what I conceive as White culture". In fact, the shift from "white supremacist" to "white separatist" or "white nationalist" has been a very deliberate project by white supremacists, and I suspect the same is true for (ethno-)nationalists of all stripes.