Playing Dom without magic is like ...well, making a car race on 1st gear !!
Yet I'm surprised at the build rate you're describing : what was the map size and what were your gold income ? Did the AI cast some globals that could have changed things ?
Building 100 Jotun a turn costs like 4000+ gold, with upkeep only of 100 giants at 500+ gold, I can't see how it's possible to reach that except very late on a very large map. And I didn't even mention the resources problems...
I'm not sure of the kind of bonuses the AI gets but they don't attain such rates.