I've only done a couple of races but I'd say that, at the moment anyway, the AI behave similar to what you'd experience when racing online on a public server, rather than simulating 'proper' racing drivers.
Too many mistakes / late braking / barging happening.
Then again, if that was the feeling that Kunos was going for, well then they've nailed it
And I'm not sure if anyone else here is getting this, but with the latest build the 0.5 second pauses / freezes increase
dramatically when racing against the AI.
I've always had these freezes with every AC build. Even with the tech demo. Might try a reformat over the weekend to see if it helps.