The laser disk were analog data, some some stuff is lost when comverting to digital (both mame and daphne).
Mame is compressed, but it's sampled at a higher res, and it's a lossless compression.
The Mpegs are compressed with a lossy compression, and are sampled at the DVD resolution.
Besides that some games have a few mpegs versions out there of differenting quality (self converted, retail dvd, and HD versions), and cube quest is not in daphane, the video quality in general isn't very different between mame and daphane.
I'm not saying they're exactly the same: they're not. In some places most people can't tell the difference, in other you can see the differences, and of course the HD version is higher quality than the original arcades so is better image quality than mame. Some games run only in mame, but more run only in daphane. but the games that are in both, technically mame is slightly higher quality.
Never the less, mame needs more CPU power than daphane, more hardrive throughput, and more disk space.