I had an old metal very well regarded 50 mm prime, 1.4 f. I also had a modern plastic 18-55 mm kit lens, high f (starting at 3.5). But the colors on the modern zoom lens were so much better. Hard to explain, but they just looked better, kind of like a DSLR photo has "better" colors than a phone photo. It was very confusing, I was expecting differences in sharpness maybe, but not in colors.
A lot of that has to do with coatings modern lenses use to correct for chromatic aberration, but also how they minimize loss of contrast from light bouncing around inside the lens. It really is incredible how much a lens affects the final image.
It's all about the glass. There's an old saying with cameras and lenses: buy the glass, rent the camera. Cameras change quickly, but lenses remain for a lot longer. Lots of comments in this thread talking about how they prefer the older lenses. Each series of lenses have a "look" to them that people become attached. Modern lenses are approaching 0 distortion in color/sharpness/etc. For some users, that's what they want. For others, they prefer the softer looks. So find the lenses you like, buy them, and use them on what ever camera you can.