This has nothing to do with the JJ films, and their plot hole riddled excuses for scripts.
From what I remember, the katra was transferred to a Vulcan so they gain their knowledge, since they can connect minds. When Sarek believed Spock hadn't passed on his katra to Kirk, he said that everything that Spock knew was lost. Sarek was all pissy to Kirk because he thought Kirk hadn't brought that katra/knowledge back to Vulcan.
Transferring the katra to a human was a unique and rare circumstance, since obviously the human brain wasn't fully compatible with the Vulcan mind. Especially McCoy's.
I believe the ritual at the end that was considered legend was the transference of the katra to restore the original unblended Vulcan mind as they did to bring back Spock, since usually you're just transferring the "katra" to merge with another Vulcan's mind; you're still dead and gone.