Jocasta may be T'Challa's Protection equivalent, in that they allow you to tutor a card in your discard pile for later use.
They both have a THW of 2 with 2 consequential damage. Assuming that you save their last activation for a Villain block, they can both deal 2 damage or remove 2 threat (although T'Challa is a bit faster in the damage dealing. T'Challa also has 4hp, which could possibly be used to block twice against a low-ATK Villain. The biggest difference is the cost: there is a mile of difference a 4 cost and a 3 cost card. What does that extra cost mean?
There should be some discussion about the usefulness of their associated events. Jocasta is less expensive and is likely more playable, but can only find (defense) events. They are all designed to prevent damage in some way, and a few can deal a bit of damage as well. It's rare, however, that a particular (defense) Event will make or break the game. Among the available (defense) events, only 11 are non-Signature cards. There are a few outstanding Hero Signature cards that Jocasta can grab, such as Spider-Man's Backflip, Captain America's Shield Block, or Venom's Mass Increase, allowing you to completely negate an attack.
Black Panther is more expensive and harder to get on the table, but can grab any Leadership Event. Leadership has some crazy events that can make or break a whole scenario (Avengers Assemble, Blaze of Glory, Lead From the Front, Mass Attack, possibly a Sneak Attack, perhaps even a well timed Make the Call). Leadership can put a lot of Allies on the table and then use them to do something (draw cards, deal damage, etc.). Finally, Leadership has the option to build a Sneak Attack deck, putting T'Challa into play for a single cost, although you lose the flexibility of sitting on that Event past that turn.
All in all, I still rate Jocasta a solid B: She affordable, can deal 2 damage/remove 2 thwart, block an attack, and give you a (defense) event that suits your situation.