gzipping is cheap, but it's not a very meaningful indicator of anything. It only refers to bandwidth and only for the first site visit. Even for js-heavy sites all the minimized and gzipped javascript put together will be smaller than a single png file.
That the library doesn't have dependencies is much more important, because then it can be loaded in parallel with other libraries. That matters a lot for performance.
Labeling everything in their gzip size (without the real size) is a bad new trend in my opinion. It feels like an unfair marketing practice since older projects won't mention gzip at all. I use gzip, but I don't think of my project in gzip numbers. The biggest issue I have with it is that now if somebody explicitly does not state whether or not they are talking about real size or gzip size, is likely that both of us don't know which size is being talked about. It feels like Fahrenheit and Celsius both being used unlabeled. I still think in real size, so it's an extra conversion for me when people use gzip only.
That the library doesn't have dependencies is much more important, because then it can be loaded in parallel with other libraries. That matters a lot for performance.