It could be argued that with a larger color palette from which to choose and with transparency and multiple backgrounds, not to mention more sprites to throw around, that, artistic concerns aside, the SNES was technically capable of better graphics. It also had more VRAM, which also helps a great deal. That said, I think the PCE was more than capable of keeping up enough to be in the same field. The PCE was not wholly inferior, and some of the Hucard games did show the available power off. Download and Magical Chase are two that come readily to mind. Psychosis is rather colorful, but I'm not sure colorful is adequate by itself, given that even the color-limited Sega Genesis managed to host a number of very colorful-looking games.
I'm not sure limiting the field to Hucards only is really fair, anyway. Because the SNES and Genesis lacked CD-ROM attachments, they used mappers to generate very large cart sizes, while the only large HuCards were Street Fighter II', which was graphically very close to the SNES version, and the Arcade Card. Since the SNES and Genesis had larger cart sizes they could put lots of graphical (and auditory) data on the cart and simply pull it when needed. The only reason you didn't see large cart sizes on the PCE was because it was simply far cheaper to release a CD than a mapper-equipped HuCard. If more large HuCards were released, some of them might have had better graphics than some of the CD releases. It has already been discussed in previous forum posts that SFII' might not even have been possible (at least not unadultered) with the Arcade Card, due to it needing so much readily available data, more by a little than the Arcade Card had on tap.
Let's face it. The CD-ROM attachment and the various system cards didn't add any graphics hardware to the system. They just provided additional storage space for data, meaning, with the SuperCD, you could dedicate a whole 8 mib at a time to a single level, or even more than that if you were willing to split the level with a load point. Some CD and SuperCD games aren't much larger, if they are larger at all, than some of the largest SNES and Genny cartridges. So, again, redbook audio aside, a HuCard only challenge is even MORE apples to oranges than simply comparing the platforms.
