@Kronzky Sorry, but i give up (but read to the End please).
It really seems to be a "Problem" with the F1 67 Mod, in Combination with this bumpy Track.
The Mod has 7 different Models with 7 different Physics (i think they've been made in a Way, to match the real Series) and i haven't checked if also a Talent File is involved.
I let the AI make a 40 Lap Race, where in the End some Cars have been lapped 1, 2 and 3 Times.
And that also affects the AIW Creation.
If you've found a better Line at some Part of the Track for one Car, the next One stills slows down there.
In the worst Case, you would have to create separate Lines for each of the 7 Models and with that, you probably would have a Dia-Show with 25 FPS, because of a very big AIW File.
But there maybe is a Workaround that you can try.
I've saved the Rubber File from the 40 Lap Race and gave it the Name Kronzky_Rubber.rrbin.
Download it below, and extract the zip File into the Folder ..\rFactor 2\UserData\player\Settings\Belgiangp_1960S_Lf
for the 1960 Layout.
Then start a Race and in the EDIT SETTINGS (Session) Tab, select the Race Tab, set "Weather Preset" to Scripted and select "Kronzky_Rubber" in the below "Real Road" Selection (Screenshot below).
Then start the Race and check, if that improves the AI Behaviour.
You can also create own Rubber Files, with even more Grip, if necessary.