Even modern desktop Linux pales in comparison because although it’s technically possible to change anything imaginable about it, to do a lot of things that extensions did you’re looking at at minimum writing your own DE/compositor/etc and at worst needing to tweak a whole stack of layers or wade through kernel code. Not really general user accessible.
Because extensions were capable of changing anything imaginable and often did so with tiny-niche tweaks and all targeted the same system, any moderately technically capable person could stack extensions (or conversely, disable system-provided ones which implemented a lot of stock functionality) and have a hyper-personalized system without ever writing a line of code or opening a terminal. It was beautiful, even if it was unstable.