The rewards probably should be a little better for both the game time and mental strategy juggling time invested. If it's a simple question of the rewards being worth the time, the answer is no...
There's so much more to it though and if you enjoy the game then the ability to have battles against decent strength opposition is great ( unlike gw ). Having to come up with clever counters to teams because no one's roster is perfect is immensely satisfying when it comes off . When it doesn't, it's a great learning experience. Beating someone with a far superior roster is a great feeling and just adds to the fun.
I feel like that then translates to better tw performance which helps everyone in the guild.
I think most of us play the game because we enjoy it and for that reason I love GA, but if for some reason the game has become a chore and you want to invest the minimum time for max rewards, then this mode would fail an ROI test.