Almost sure it’s not the problem and my current testing seems confirm it.
There’s a difficulty scaling mainly based on number of combats done. The point is favor a lot explore, skip as many combats than possible, and use training facilities.
This should allow reach a team level 7 able to sustain difficulty scaling thanks to various OP builds.
Until I realized it, to face the quick difficulty scaling I was trying be the most efficient than possible, more teams and planes faster, do as many missions than possible faster. This was only leading to an even faster difficulty scaling.
Now I know the trick, I have yet to suffer the problem. And will certainly be quite ready to face stuff when it becomes big.
EDIT: This even setup the plan for the easiest path, the easier path is the faster path, so it’s rush only one faction to get its end and get game end a lot sooner. For sure you can’t totally rush it, there’s trick to find to speed up factions wars. If it’s possible, rush one faction, rush factions war, rush to end, easier path to beat the game.