That’s a difficulty, not a balance issue. If you feel like the challenge you are facing is above your expectations for the difficulty you are playing on, you should definitely start a topic on that. I can assure that the devs will be very interested in that kind of feedback.
However, the answer to high difficulty can’t be obscure skill combinations that result in a single soldier clearing the whole map in a single turn on his own.
First and foremost, it’s not fair to the new players (particularly casual players who are not familiar with the genre), who don’t know about these skill combinations.
It’s also not fair to the conventional players who are looking for a reasonable tactical challenge and expect the devs to balance the game, not to have to balance it themselves by applying self restrictions when necessary.
Anyway, if you are interested there are several topics dedicated exclusively to this issue. The most recent, if I’m not not mistaken, is this one: Think combos are OP, don't use them - #4 by VOLAND