> Maybe Ubuntu just has gotten "bloated" over the years and everyone has failed to notice because all PCs are overpowered these days

When my terminal after starting unity is pid 12000, you can guess bloat has occured. Even on my arch boot my terminal after auto login through the x virtual console is pid ~500 still.

Also, Unity uses at least 300Mb of memory, and composting. Compostinggggg.

Most of the inefficiencies in a modern Arch distro, for example, are build around plug and play mostly I think. Udev, systemd, dhcp, etc are all designed to gently allow arbitrary hardware arrangements without interrupting the experience, but cost performance to determine what is available and constantly babysit the environment.