Quote Originally Posted by Vinyadan View Post
If the club (or, I would say, plank) isn't larger than the blades, yes, they do.
That removes the problem of having to push something blunt through. There's still a very fundamental problem of volume displaced - which is the cross section of the neck along the cutting plane times the thickness of the blade used to cut*. This applies to blades in general, and is part of the reason you get the extremely thin blades in falchions and the like.

A machuatl goes very much the other way. They are exceptionally sharp, and they likely tend towards higher angular momentum (though they might well have tapered; it's a tricky design that involves a lock of skilled obsidian-knapping, but there's no reason to think the people making these weapons weren't good at it), both of which would help with the cutting, but that extreme thickness doesn't.

There's also the small matter of how the cultures that used and developed the machuatl didn't have horses, and didn't have a lot of time to develop weapons to deal with them. That's not to say that they couldn't kill horses just fine, just that straight up decapitation was unlikely.

*There's obviously a level of simplification here.