I run rebel swarm lists (a-wings) and I can tell you right now what would lock them down is area damage and escort.
Dengar is a must...giving EVERYONE counter is pretty big. Throw in Howlrunner, interceptors and maybe a few advanced and you could just about wreck anything.
Area damage can be effective, mauler is real good...but the meta is slowly leaning towards locking him down...you need to combat numbers with numbers as there are so many one trick pony squadrons.
I'd do something like...Howl/Dengar/Black Squadron/Valen, and the rest advanced/interceptors....move it together and keep gonzos pushing it together.