It is derogatory. Virtually no Americans call themselves "USians". It's nigh unpronounceable (it sounds like "US Asians") and only seen on the internet in the context of somebody with an axe to grind against America (as above.)
Some people you just can't insult.
It's impossible to insult someone who refuses to be insulted.
That's not going to make anyone happy. It's Türkiye.