If they adjusted certain parameters and fixed some boneheaded moves on some tracks, it would actually be really competitive. It was considerably better than any of the previous games in terms of player and track awareness. GT4 in particular made it so certain cars (anything FF, cars with bad brakes, cars with good brakes) lap after lap after lap would make the exact same mistakes; so GT5 is much better than that.
GT40 (and Mercedes SL, and Saleen S7, and Cizeta) at Le Sarthe would shoot off Hunaudières into the sand every time. FF cars would understeer into the walls surrounding chicanes (like on George V) every time. Cars with loose tails would spin out on certain corners every time. None of that happened in GT5 outside of specific instances, and they actually drove somewhat inconsistently lap to lap as if they were actual beings.