2B's P1 was nerfed not its P2.
6B's p2 was much better and it did more damage, you only do 2B if you are dealing with netplay or a laggy TV.
J.C>j.B does more damage than a normal combo and add more meter, so what if doesn't work on half the cast, do it on everyone you can do it on but Jin.
Jin is not worth it IMO.
To answer Zeron's question it's pretty simple, it's a execution barrier.