I never understood the paste thing on any piece of meat. I have never had an issue with the rub not sticking to the meat.
I'm certainly not the expert here, but my recollection 10 to 15 years ago was that this became common place: yellow mustard on pork butt. Didn't impart a flavor as far as I can tell.
Personally I kept trying other things:
truffle oil on tri tip (winner)
Worcestershire on steak/brisket (good, but careful not to overdo as the taste comes through on the end product)
molasses on pork butt (awesome for bark)
I do agree with you, none of it is strictly necessary for a dry rub to properly adhere to the meat.
DK