My car is NA with the OEM small brakes and M/C
I used to be unhappy with my braking performance and wondered about updating stuff, bigger brakes etc to try to improve it. I hated the soft pedal, and front wheel shake under heavy braking.
Finally I fitted RDA stock rotors (no slots,dimples etc), put a reco kit through all calipers and fitted
STOCK Toyota pads.
After draining and filling with a heavy duty brake fluid, I finally went to a lot of effort to bleed the system
several times after activating the ABS at slow speed on a gravel road.
The result - fantastic!!! Great pedal feel, smooth even braking with no wheel shake under heavy braking, and no fade apparent even during a Winton track day shortly after I did the job.
Early ABS no good?
Look, this is just my own opinion based on my own experience, but I feel that the stock ABS works fine with the OEM wheels and tyres Toyota designed it to work with, so you're probably better off with it connected if you've still got those.
However with large diameter wheels and low profile tyres it is a different ballgame especially on rough surfaces, and since many people have these on their car, I suspect that is why they disconnect it.