Yeah, the AI in FH5 basically chooses a car that matches the player car's specs to some extent, allowing you to win as long as you don't intentionally make extreme upgrades.
However, on some courses the AI seems to be unbalanced, making it significantly harder or impossible to win with cars that can easily beat the AI on other courses.
And apparently, the Baja Scramble Circuit is most likely the circuit where this trend is strongest.
What we need to beat them on this track is overwhelming grip and acceleration performance on the gravel.
To borrow from what others have posted on the official forums, the easiest option to beat them on this course is a 4x4 with stock tires like Bronco, Jimmy, Scout, etc. that are the equivalent of off-road tires.
These cars don't need AWD conversions and tire upgrades, and are basically heavier, so they save a lot of PI.
Swap a high power engine into these vehicles and use the remaining PI to improve the handling.
Then lower the center of gravity by lowering the ride height with suspension settings, and they are no longer our enemy.
We will be able to beat them easily while maintaining our overwhelming lead.