I mean, sure, in principle it could totally do that, but presumably all the copies of such erratic systems got eaten by tigers instead of successfully passing on their genes.

There's the question of the absolute effort needed in order to get the abstract reasoning system to work reliably each time, versus just wiring them into a balance where the non-abstract system dominates most of the time when the abstract system gets things wrong. Evolution will pick the easier and faster solution.

I'm not sure whether you're saying that personal identity is an evolutionary kludge (like the appendix or something), or whether it's absolutely required in order for any abstract reasoning system to function properly.

The former.