I like AI to be strong and brutal. It would be fine for it to be unforgiving if this would be the only thing that stands between player and winning the game.
Unfortunately, X-Com already has quite a number of things capable of failing game without player direct mistakes. Like 3 countries sign an alliance, undetectable USOs early on, etc.
All things combined it would be a bad experience to fight all ground combat and then loose just because of some other reason. So it would probably be better to have 1000+ combats not absolute nightmarish.