My bad! Yes Waifu2x is just a single algorithm, you are right.
The confusion originates from the fact that I was using a GUI project for Waifu2x called "Waifu2x Extension GUI" (https://github.com/AaronFeng753/Waifu2x-Extension-GUI) which other than Waifu2x also supports other algorithms like Real-ESRGAN, Real-CUGAN, SRMD, RealSR, Anime4K, RIFE, IFRNet, CAIN, DAIN, and ACNet.
So as you said Cupscale is surely more advanced than Waifu2x (the single algorithm), but do you think it's also better than Waifu2x Extension GUI?
Considering waifu2x is the name of an algorithm I assumed it was just that algorithm. There's also no mention of other models on the demo page or the Github page as far as I can see.