I'm an idiot! I tried everything, consumed pages of archaic documents on modifiers, I dug all the way over to page THREE of google search results, I lost hours of sleep, watched an embarrassing amount of tangentially related tutorial videos in which the teacher, bless them, had to communicate through a thoroughly mashed potato they had stuck two wires into,

...the solution was to update Blender. SMH. I can't believe I forgot.

For future reference, the above set-up works! If anyone in the future is having trouble figuring out Mesh Deform with Armatures, I hope these pictures and descriptions help. Just... make sure you've updated blender. Lord.

And make sure you Bake any physics or wiggle bones before rendering, as always.

The solution was to update Blender.

For future reference, the above set-up works. If anyone in the future is having trouble figuring out Mesh Deform with Armatures, I hope these pictures and descriptions help. Just make sure you've updated Blender.

And make sure you Bake any physics or wiggle bones before rendering.