No kidding. Its reliance on low-resolution MPEG-1 for video meant VCDs compared poorly even to VHS. I believe the NTSC discs had roughly similar horizontal resolution to VHS, but only about half the vertical resolution. I suppose the quality would be similar in theory, as the VCDs were not interlaced like VHS, but that wasn't my experience.
I had Star Trek II and a couple other movies on CD-I video discs, and my first impression was, "wow, I can barely make out these opening credits."
I do, however, credit my CD-I for giving me early exposure to the VCD format. I had a CD-R back before most people even knew they existed (they were still called WORM drives), and I put together a few school projects on VCD.