You're spun around, flipped upside-down, and confused as can be.
Very compelling, but have you considered
Tankie is a term that specifically refers to one particular kind of communism
No, it's used to refer a wide, vague blob of vibes, just like the word woke. The people who use it can can do use it to refer to all kinds of communists, most anarchists, and anything to the left of Elizabeth Warren in general.
that try to impose communism through the use of force.
As opposed to the kind of communism where you ask nicely for revolution? Have you actually read any Marx? I guarantee he was not a pacifist.
You can be a communist and not be a tankie
By your own definition you cannot, let alone by a definition of tankie that describes how libs actually use it.
And when people say they are "anti-tankie", they actually mean that they are anti doing anything about the awareness of systematic inequality that tankie indicates. By definition, someone who is against change/progress is a conservative, so when someone says they are anti-tankie, they are by definition expressing a conservative stance. That is, wanting to do something about systemic inequality is synonymous with having a progressive stance on systemic inequality.
Being a tankie, on the other hand, is not synonymous with being a comunist. Tankies are just one form of communist (militant).
Other way around: communists are just one form of tankies, the word is also used to refer to anarchists and some soc-dems.
It's not clearly defined at all; try to give a definition of authoritarianism that applies to all of the countries frequently described as authoritarian, but not to any of the ones that aren't, and you'll see how vague a term it is.