Wheatpasting is great. To me, the difference is twofold. Roughly speaking, you could say:
Honestly presenting the source of what you're putting out is opinion, disguising or being deceptive with it is propaganda
A method that offers 1 unit of influence per person, is opinion, whereas a method that gives 1 unit of influence over the narrative per dollar is propaganda
Like I say, I am fascinated that you don't see a problem with running a large number of accounts to create the illusion of popularity of a certain viewpoint, without it needing to be a persuasive enough viewpoint to gain popularity on its own