The debug graphs cause a tremendous amount of lag, especially when you first open them. The Alt+F3 graph has dropped my framerate considerably from over 100+ fps to 1 for a second, then around 70, (depending on the version). This makes it difficult to provide accurate fps graphs in screenshots.
It is hard to see in the 21w06a one, but there is a lag spike in the middle there. 21w06a has very bad performance on my computer to begin with, so I've provided some screenshots from other versions as well to show where it is a little more obvious.
Update for 21w08b: The fpsPie element (the debug pie iteself) was averaging about one-fifth of the debug pie. It at times was up to three-tenths.
Can confirm.