Jump with them
On a serious note:
You can't do jack shit about Lex's jump back 3
Certain characters (zod, martian,wowo) can just jump all day around you cuz of very good air control/air dashes
Certain characters have to wait a second to do their air normal to connect it, so with those characters (catwoman is all I can think of ATM) is dash in and air grab.
You can also for the most part dash in WCC air grab. Or on certain characters you can WCC d2 into a punish combo up to 50% with 1 bar (27% max no meter, 62% with 2 bars)
Overall in the end, jump backs is another pain in the ass that comes along with playing grundy