The problem with X2 is the same with any game with DLC content: power creep. The normal campaign remains the same but the extra powerful armour and weapons made it easier. Once you get them, of course. The end game basically becomes much easier.
I haven't played with WotC yet, but it sucks to hear that the endgame gets even easier. I recently finished vanilla XCOM 2 + Shen's Last Gift & Alien Hunters, and the last 20-25% was way too easy except for the final battle.
Have you played Phoenix Point? How does that compare difficulty-wise?