Here's my tuppence. They are two different systems. For max autobrake operation you need antiskid to prevent wheel lock. So the autobrake system requires antiskid operational. And as you suggest, antiskid is more than desirable in RTO with max manual braking effort. Hence the huge penalty on RTOW with antiskid inop (7,800 tons RYR policy), as far as I remember it's not even allowed on a wet rwy.