The negative-vs-slide film argument has been around a long, long time.
That is probably because not many understand the technical differences between the two.
What makes many think that slides have better color than prints from negatives is that they often really "pop" compared to prints. This is due to the fact that high contrast and high saturation is built into them so they look good when projected. This does not mean the colors are accurate. Such enhancement can often distort colors slightly. Negatives are low contrast, giving them greater dynamic range and preserving color accuracy.
Both negatives and slides have dye impurity issues which degrade colors a slight amount. They are masked in negatives but not in slides. When a negative is printed, only the dye impurities in the paper, which cannot be masked, appear in the print (hardly noticible), as the impurities in the negative have been neutralized. But when a slide is printed, the impurities in both the slide and paper appear because of no masking, compounding the problem. Also, the high contrast of the slide appears in the print as well. All this results in a noticible degradation of the image. To be fair, prints made from slides can(could) look acceptable and even striking to the viewer, but in this discussion I am talking objectively not subjectively.
For any use except viewing directly or projection, the high contrast and lack of masking is always going to present quality problems when compared to negatives.