So, the message is still there under 1.8.That is right, I'd say 99% of people just use steam, seeing no reason not to. And of the 1%, most probably don't notice the inactive AI.
Anyway, I've just now received clearance to say that Paradox (well, Wiz really) have fixed the recruiting/building AI so that it works the same whether Steam is present or not. You may well still get that message on startup, they haven't told me either way.
Can you confirm that the game will run flawlessly without Steam, even though the launcher is warning us that it won't? I can't seem to find the non-building AI bug in the changelog.