Diskin's stuff is good because it is his own and it is for the fans, not the team.
I respectfully disagree to a point. Yes, he is inspired because it's his team, but he also just plain gets design. That magic sprinkle dust that makes him a good designer doesn't just happen because he is a fan. As well, he did design the new Thorns crest for the Timbers which would in a sense disprove your theory. The guy is just plain good no matter what he does. Not that I don't understand the delineation between club and supporters. I think it's important for both.
I agree that these are just good designs. However, the ethos of the propaganda is the ethos of the Timbers Army, not the Portland Timbers. That ethos would be much different if it were funded by the team. But because it has organically grown out of fan support and DIY, it has developed a particular brand to it. If the team were paying for fake propaganda about their rivals, it would be really silly to be honest.
As for the Thorns, that doesn't have the same feel as this propaganda. It's good, but it's not the same.