The Classic Mac OS model in general I think is the best that has been or ever will be in terms of sheer practical user power/control/customization thanks to its extension and control panel based architecture. Sure, it was a security nightmare, but there was practically nothing that couldn’t be achieved by installing some combination of third party extensions.

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.