White nationalism/supremacy/dominionism has a century-plus-long history of extreme violence and terrorism behind it in America, and continuity running back to before the Confederacy. Antifa is relatively new (especially the "Portland" brand) and rather small, with less continuity to its anti-fascist roots. These are probably not good candidates for comparison on any level, especially as their tactics are completely different.
Antifa could easily become more violent than it is, or be cracked down on when certain mayors grow a brain, or it could lose popularity, or even make way for something new that's more or less of a problem. The fact that nobody has died yet (is that true?) doesn't indicate that people won't die, and trying to rank the two phenomena as if each is just an unfortunate end of the wings of our cultural divide seems irresponsible and has the tendency to drag people into accidentally defending something in a tribal way that they really despise.
I just don't like anything about the comparison, true as it may be.