I agree that too many "strategy" games devolve into optimizing spreadsheets once the rules are known.
I don't think Dom2 suffers that problem. I think that even with perfect knowledge of the game, there'd still be a lot of "magic" to discover in tactics (equipping commanders, casting spells, and organizing armies) and strategy (pretender design, running campaigns, and reducing the other side's ability to fight). Most importantly, I think Dom2 has so many options that there's still lots to discover in how to deal with a *specific* way an opponent is fighting while trying to make him fight the *specific* way you can win.
As to what generals know, sure, even modern professional armies don't have stats on their troops and weapons. OTOH, we don't have staff officers, field exercises, RDT&E units, and years of personal experience commanding men. So, we use stats and tools (hail Saber Cherry and Edi!) to get the information in other ways.
(Oh, RDT&E == research, development, testing and evaluation. Guys who invent new weapons and tactics and see how well they work.)