Are there any Jag demos that look like they couldn't be done on a SNES?
There were some games that dropped around 2000/01 that were pretty impressive visually. Skyhammer and Battlesphere come to mind. I think that era of stuff was mostly finished in the mid 90s before Atari went under, so it just sat in purgatory until a publisher came along after the fact. Not sure how much actual additional development Songbird or whichever company did to that stuff before it was released.
The vast majority of homebrews I've seen on the Jag are fairly primitive graphically though, and look no better than SNES stuff. And then there are a ton of Atari ST ports that have come out. But the Jag hardware itself is fairly powerful, and was far ahead of the SNES. Its failure was due to the business incompetence of Atari, not the actual console.