Windows Update's slowness is a feature more than a bug. The underlying Background Intelligent Transfer Service (BITS) is still such a cool piece of tech even if it has been ages since any web browser let you send low priority downloads to it or an RSS reader was built on top of it. (Both things that existed and were cool, especially in the dialup era where bandwidth was scarce and irregularly connected.) It's designed to prioritize active user needs over pending downloads, throttling itself based on CPU activity and bandwidth usage and download quotas and battery state and expected runtime and now things like estimated energy mixtures (why not download big things when energy is greener?). (It really does download faster when you are not looking, that's what it was designed to do.)

A key aspect of many Linux package managers such as DNF or APT is that the repository is just a static website. The server doesn't need to compute the delta between where the machine is and where it should be - that's done in the client.

That, of course, imposes some limits WRT package visibility and other policies you might want to enforce - you can't easily limit a certain set of users to a subset of your repo.