Hork-Bajir are probably heavier than people, and that weight from the look of it is muscle. An arm blade on this things basically is an ax.
For the thing like the hyena: tons of force behind the bite, but the surface is for shearing and crushing more than cutting. They can tear meat, but teeth aren't really made of that clean cut like a blade.
Which brings up the: what exactly are the aliens blades made of, and how sharp it is.
If it's something that will keep integrity, being propelled by MASSIVE muscle (a hork-bajir should be able to punch you out, and look at Elfangor's tail on TAC: it's a friggin python-that's a lot of power) that cutting through bone is
I'm gonna stop and change that
First: flat out yes, a good blade can cut through a most of a body. There's some stuff on line you can find with livestocking being put done very quickly with a sword.
But for alternative, lets do this. They aren't cutting bone.
They're cutting ligaments, muscles that connect bone. Bone's aren't held together by other bones, they connect by soft tissue that I think you'll agree is "easy" to cut.
You don't have to cut a bone in two, just cut the ligaments at the space between the bones-and I attest these alien blades and muscles can do that- and the bones separate.
So no, it wouldn't be as clean as cleaving a bone might seem, but there's more than one way to cut off a head.
