>the classic theme was a lot leaner on system resources
maybe, but it probably also made things run slower because it forces everything to be done in software rather than hardware.
https://devblogs.microsoft.com/oldnewthing/20130327-00/?p=48...
>Starting in Windows Vista, a lot of visual effects were offloaded to the graphics card. Consequently, the impact on system performance for those visual effects is negligible, and sometimes turning off the effect actually makes your system run slower because you disabled hardware acceleration, forcing operations to be performed in software.