Used to do a fair bit with Jet2 as well, but since they grew the Jet2Holidays brand, they soon stopped. Then they used Monarch, so since went under, it's either U2 or FR. Ryanair probably could offer allocations cheaper if they wanted to, but they're happy to sell all of the seats themselves, leaving Easyjet.
I still suspect more of a TUI/Easyjet tie up of some kind coming up soon