Yep, and it popularly is. I reserve my right to pedantry!
By all means!
But somehow I have managed to miss your point, Mr. Drill. He’s just saying that you can tell you’re dealing with a real Marxist when they use the adjective “Marxian” instead of “Marxist”, since that’s insider lingo used mainly by true believers. IOW he’s letting us in on a tell (although most seasoned Freepers probably knew it already).
You would probably agree with this, so what is your objection, if I may ask?