I think it's pretty obvious that antifederalism (actual federalism)(fixed it)
has been politically irrelevant, as you point out, for a very long time.
Well, as long as you admit your political beliefs are irrelevant, I have no choice but to agree with you. Of course, the reason you give is specious. You can't beat something with nothing. The Anti-federalists weren't able to come up with an alternative document back in the 1780's and whatever heirs they have still can't come up with that alternative document. For the sake of argument assuming the Constitution was all bad, wrong, evil, pernicious, (insert additional negative adjectives here), you would think the Anti-federalist Constitution should be leaping off their pens... well, to update the image leaping off their keyboards. Yet the mountains groan and bring forth... nothing, not even a mouse.
Even if there were no chance of implementation today, you would think Anti-federalists would memorialize their improved document for the sake of future generations.
I'm certainly not going to hold my breath waiting for the Anti-federalist unicorn.