I'm in LMA in 5 worlds.
I began fighting heavily in GE starting in EMA.
#1) By far the best advice I would give, is get Rogue Hideouts!
#2) Learn which units are most effective against whatever enemy faces you.
When you get to wave battles, where there will be a second attack wave, make certain to look at those troops, to make sure you put out a balanced-versatile attack force.
The troop combinations I use are always determined by studying the enemy unit I'm facing.
My preferred units are with 1 Mounted Knight, and 1 Heavy Knight, with 6-7 Rogues.
Of all the ranged artillery units available to me, I use Catapults/Ballistas/Trebuchets/Cannons the least.
Of the various ranged units, same thing: Archers/Crossbowmen/Longbow Archers, I don't use them a lot.
Saying Mounted Archers are useless is wrong, as any general statement tends to be.
If you are facing all Archers/Catapults, 7 Rogues with 1 Mounted Archer is a wicked offensive unit.
For instance, I'm in LMA, but in the early battles of GE level 1, I can still defeat certain enemy troops deployments, using those Mounted Archers, with Rogues.
Every unit can be used effectively, as long as you are able to field Rogues with them. And you have to understand how to use them tactically, of course, which only battle experience can give you.
When I first began facing the wave attacks, I thought they were impossible, but as I continued to fight, and really learned the effectiveness of all my various units, I learned how to do it.
I fight all 3 levels of GE, 48/48. But it's only possible because of my Rogues, CDM, Zeus, CoA.
FWIW, I only have Traz in 1 city.
I also have just started a new city in S world. Haven't decided how I will go about competing in GE, as I have zero troops, no Rogues.
But I probably won't bother with GE at all until the next USEFUL event, where Rogue Hideouts are available, and then only if I'm able to win some of those bad boys.