I think the stock Notepad in Windows 10 is perfectly fine and speedy at least, I've never considered it too slow unless I open a huge file with word wrapping on.
Notepad2 is my all-time favorite though. It supports key features like line numbers and directionless search, but is much closer to stock than Notepad++. [0]
If you edit the same 1KB file on each computer side by side the 30 year old computer will be more responsive than the modern one.
That's what people are taking issue with.