You followed the rules and participated in the jam. My career has been as a graphic designer and illustrator, just to make clear what kind of background this opinion is coming from. It's totally fine to use assets and support other artists if its within the rules. Being able to put multiple assets into a game and keep it cohesive is a skill in itself and shows an artistic eye. I used free, paid, and modified assets for my entry and credited them so others could see their work. I think that's an amazing part of game jams and indie development. While creating your own art can be fun and rewarding, I'd rather play a fun game whether it was made with original art or not. That's just me. I love that this community can bring people of different skill sets together to share a common passion and support one another. I think the suggestion that you are undeserving of anything for your hard work is pretty short-sighted. Again, just my opinion.
I take back my harsh phrasing. "Within the rules" is the operative phrase here. I also like how you said fun is on the chopping block, NOT art skills. I'll take a step back and reconsider what a Game Jam should be. The ones I did in college were in person, and the skillsets were pretty 50/50 art and code, so making a team was expected. They also had comparable skill levels, so nobody blew anyone out of the water. This Jam by comparison has a pretty huge skill level spectrum, so I get whiplash from people sharing their first game ever and then to this one, which looks incredible and the polish blew me away.