Consider the effect:
Max out the compression, suspension slows way down. The dw-link definitely doesn't need this type of a crutch (neither CC's RCA nor a real lockout), agreed? And changes to compression settings won't influence sag.
So now you're hammering on the flats, you've pretty much eliminated any sort of small bump sensitivity by activating the psuedo-lockout, and if you hit a series of roots or some other protrusion, you suddenly find your back end flying off if it, rather than absorbing it.
So I'm leaning towards this being a bad thing for the flat-running XC situation you're describing. You just made your bike a softtail, in the riding conditions it should shine in.
Keep in mind that even a bike with average to mediocre suspension, featuring a shock with a lockout, the rider is apt to use the lockout on slower climbs, when the bike isn't going to go fling itself skyward when it hits some terrain -- but the rider is going to unlock it and let the mediocre suspension do its thing when hammering the fast stuff.
I'd suggest your disappointment is with your tire and/or wheel setup. Check tire pressures. Look for some rubber with low rolling resistance or lighter weights.