I think I'm a different case compared to others, in that I'm not after laptimes or game results/recognition. I'm only interested in the best immersion, because I ride in real life and look for something that can relate to the real life experience (with a PC game), while being limited to a gamepad (but with analog controls for brake and throttle).
So, please consider this for the rest of the post.
IMHO, in this game the combined brakes are not really what you encounter in real life.
IRL, the front brake does about 70% to 90% of the job, and the rear brake is mostly used as a "brake compensator" or balancer.
(which is what it mostly is on a real life sportsbike/racebike)
The rear brake in this game works like a clutch, and not like a rear brake.
Meaning, using combined brakes in this game is comparable to an action where the clutch and brake levers are pressed, all at same time - it's unrealistic and somewhat counter-intuitive.
Therefore, I find using split brakes is the only possible way to go.
(to me anyway, YMMV)
I use only the front brake to brake, and I try to be fairly cautious and gentle with it, like one would be IRL. After setting a very low sensitivity (on analog trigger) it works "OK" in terms of effectiveness and immersion.
(braking behaviour here is a different mattter, more related w/ physics issues)
ATM, I do use Anti-stoppie at 'Low' as riding assistance, to counter the lack of feeling (which, TBH, I think one could only get with a real life brake lever).
I then only use the rear brake ocasionally and, funny enough, I treat it exactly as a clutch.
I use it mostly to "spike/instigate" revs (like you would IRL on a 2-stroke), or pop-up a wheelie. Sometimes also for "blipping" the throttle when downshifting.
(for the non-bikers, think of it as the motorcycle equivalent of the "heel n' toe" technique) So, used mostly for fun and appreciated for that!