Moved to Feedback/GW.
And I confirm what Huatimus said : Devs have several times confirmed the opponent's choice is still dependent on the old power computations.
And that GW is meant to be a challenge for your whole roster. Focus on more than 5 toons (anyone two gear levels than your best toon, or lower, is near useless), build multiple squads with them (the more, the better - and by squad, I mean well-functioning ones, with synergy, not random assortments), plan your strategy on the whole 12 nodes, build TM on your best squads (and protect them from harm/waste).
In a sense, GW is the opposite of Arena. To excel in Arena, you have to focus your development on a narrow group of toons, but to excel in GW you have to broadly develop your roster.