Filoni and Witwer have said Maul's powers were diminished. However, at least in Legends, we know this was offset by the growing galactic dark side nexus, Maul's own growth, and (sort of paradoxically) Maul experiencing and overcoming the ordeal itself. He's said to be as powerful as he was in TPM in "Revenge" and more powerful than ever by "Revival." Even in Canon, I believe Filoni has emphasized the growing galactic dark side nexus as to why Maul's more powerful now than before, though I would need to recheck. Either way, getting chopped in half certainly diminished Maul's potential power, which was originally greater than Palpatine's own apparently.
Originally posted by Scizard👆
I don't think less midichlorians from limb loss is a thing, atleast in canon.
The tweet you're referring to is Chee echoing someone asking him about the Lucas quote. He's not him making a statement on the matter. In fact he says he doesn't track power levels at all. Also, the initial question was about G canon which doesn't exist in Disney canon. It's very probable he talked from a legends perspective as the question was about legends