Lol, EXACTLY.
The normal difficultly level sucks. I'm not sure if you can get the achievements with any other level but, "normal & insane". I played the campaign again with "skilled" and it was better, but still had a bit of what you explained above.
I found that in the campaign you MUST have human players on your team against bots. Then it becomes WAY easier. I think even All human players verse bots could beat "insane".