So are MECs ever a problem for anyone? The first time I encountered a MEC was after I'd gotten Haywire Protocol on my best specialist, and I've never failed a hack on them to take control so far. I just take a specialist with Haywire Protocol eith me on almost every mission now, and whenever I see an enemy MEC, my first thought is "Ooh! They're bringing me presents again!"
I mean worst case scenario, they shoot the hell out of it before it gets a chance to act, and then it's still out of their hands permanently.
The first time I met them they were annoying because I didn't like their armor, and armor was frustratingly annoying.
At this point I'm enjoying their existence tremendously. Makes my life significantly easier, depending on the situation. Just had a mission where I saw two MECs and a trooper, and I take over the regular MEC (there was also a Heavy MEC, but the odds were a little too close to be a good idea). Overwatch takes out the trooper, and I use the MEC to detonate himself, the other MEC, and the ground they stand on.
Unfortunately it A) activated a second pod, and B) got killed by the Archon it activated, leading to C) the Heavy MEC raining explosives on my squad. None of this would have been too bad, except D) all the falling and exploding caused a bad glitch, and it seems I'll have to restart the mission because all my troops lack animations and I can't end my turn. Oh well, when I restart it, I'll know what to do: A) try my luck with the Heavy MEC, or B) don't blow up so many buildings.