well, I can say the car handling depends also on what for Automobilista game version the user have, I suppose... see below.
to be honest, at my Steam game version all Reizas cars seems to me they are undrivible with a keyboard control - which is for me as a 2D/3D mod stuff maker my default sim game control
my G25 steering wheel mostly sleeps patiently in a dusty box.
when turning the default F-Vintages cars left or right it tilts like a boat on a stormy sea. even the super-exaggerated GPL game car handling is a lot stable comparing to this
Ive tried a few another AMS default cars, including something like Audi R18 looking car, and same result, it tilts like a boat when turning left / right, just less a bit, comparing to the F-Vintages.
and now the important thingy: Ive got from one friend some stripped AMS game variant, Steam independent, for internal testing our mods there too. what is interesting is the physical results made at this game variant - Ive made a copy of the F-Vintages into this game, out of a pure curiosity, ran it there and the "tilty boat" effect was a much much less noticable.
as to our F1LR cars, they runs at the Steam AMS game version very well, however they acting just bit more "wilder" comparing to the AMS stripped game variant. therefore its all about the current game engine updates, I would say.
note: original Reizas car physical files (hdc, tires, suspensions) and sfx soundset files are encoded into the AMS main exe file, to be protected from modding / ripping.