Count Dooku using Sith lightning ruined the prestige.
I agree. That should have been an extra-high ability power unique to The Emperor.
Speaking as an A:TLA fan, I’m glad the show limited lightning bending to just Azula and Ozai (i.e., two royal family members who were bending prodigies). Korra did away with that limit (while the Kyoshi novels made it even rarer than the A:TLA). Still, it’s more understandable than making Sith Lightning so widespread.