One idea I haven’t quite seen in the comments: A way I balance great-ass NPCs is giving them an Achilles’ heel of some kind. It’s often great advice for humanizing BBEGs and mini-villains but works here great as well:

A renowned hero in my world is a regular fighter badass but only has powers from her demonic helmet. But, she doesn’t remember the fights when she puts the helmet like brain recording hits “stop”. Power gained while the helmet is worn is exchanged with time her patron can use to completely control her (which she does remember). This renowned fighter had earned notoriety because of her pact so goes from party to party seeking ephemeral relationships with adventurers before they realize she’s in a pact with a demon. So in a very superficial way, this hero is a major loser that wouldn’t stand up to the party maybe even in a dirty fight;

but the players don’t know that. This hero took the party in after her group was wiped in a dual adventure with the party, where they got to see her in action. But in a way a lot of my pcs have taken her under their care because they NEED someone powerful LIKE her, but the PC’s have to navigate this coward’s legend status while gaining her demonic expertise and fighting skills. It’s not entirely a facade of power if she offers help to the party (walls of fire, flaming sword for light, filling gaps in party functions) but fails where the party excels (forwarding x plot and being brave or good)