This explains a lot! I thought there was something I was missing about deep gates since they seemed to make the game really hard -- and the part that I was missing was that you're supposed to have an option to wait until you're ready to attack them. I'm really looking forward to the build that fixes this.
I've hit the same issue multiple times. My experiences:
They can be particularly deadly in the early game.
Attached is a screenshot of a game where I hit two of them on the same turn. Neither was visible before they were activated. Note that Demonica has not yet emerged.
When combined with evil outposts, robotic factories and/or impasse tiles, they are much, much harder. This will also be somewhat addressed when you always have an option to wait: You can go in from a different direction, build up a big presence of resistance in the area before you activate the gate, and/or wait until you're high level.
