Xpiratez is difficult to play like a modern CRPG, without an insane anount of metaknowledge.
If you go into it and expect casualties to be rare, or that there will be no disastrously punishing happenings, yeh, it is hard. If you go into it and attempt to YOLO it, it also gets hard because it is so long, so lucky streaks will run out.
Playing it in a slow but deliberate manner, treating units as expendable, and going on even after serious setbacks is easy.
That said, OXCE itself is a very complex engine that also adds complexity to the mod's complexity.
There's really no argument to be made that the game is easy. It is not easy to learn (especially if one never played 1993 xcom), it is not easy to swallow psychological defeats like losing a favourite gal, or a base holding all your treasure to crackdowns, and it is not easy to unlearn modern games streamlining.