Agree with the premise of the OP, rebels are by far the best with multiple options for awesome teams, but .....
The empire will get some more toons with the movie as well I'm sure. I am avoiding all spoilers and such for the movie so I don't know the name of the guy in white or the other -troopers that are there, but there will be some.
Not sure when the emperor event will come back, but him, Vader and the new guys will probably be pretty effective when added to shore trooper.
Vader will eventually get a rework or a special version (like emperor, general kenobi)
Jedi already have two ultra characters (Yoda and Gen Kenobi) and are viable
Jawas and droids will get some more help and are already viable.
First order will get help in the form of Snoke and some others with the movie next year. So will the resistance with either old Jedi Luke or light saber Rey and possibly others
That leaves a couple groups that are weak right now - night sisters, tuskens, etc that will probably never be viable as a full team unless a lot of work is done for them
Also it wouldn't surprise me if the heroine of Rogue One is a scoundrel and not a rebel (which they should've left Lando as) so scoundrels might get a boost as well
