Corsairs are really powerfull, and the fact that they relly on possessions (which are far harder to discard) then on conditions makes them a big threat (to not speak about
Castamir and Marauder).
But even so they are not broken.
Roll of Thunder (That may be why 80% of my decks have Gandy), Arrow Slitz,
BRC and the "splashable"
Derufin are quite effective against them. Also Direct wounding decks kill the biggest guys before they ever imagine to do any evil stuff and some Gondor artifact based decks with biggers companions and pumps can be hard to stop.
Sadly Corsair destroy many kinds of decks, but not even close to the Lady Redemmed +
Cirdan brokeness.
Just having her in a deck doesn't give you a certain victory (or lose if you opponent plays it) but it simple reduce many shadows to worthless cards played in order to get more freep cards to run. I played against a deck with her these days and i won with a shadow kill, but i was playing one of the few decks i have that doesn't mind with her presence...
I would bane her to prevent that you may only see 2 or 3 types of shadow in the tourney, more diversity is more fun in my opinion.