If the "Ashcroft diffs" you mention = ATBs: they are not necessarily better than unlockers like the detroits. They are very different and not necessarily suited for the same use cases or same driving styles. It depends on your use case and needs - which is "better".
Unlockers, and locking diffs, do give a full hard locking of left to right axle. ATBs can never fully lock up like that. If your use case requires a fully locked diff (even if only for several minutes on occasional hard core trails - then ATBs don't cut it.
If your use case involves a solid desire for some degree of left/right torque transfer on and off-road: then lockers and unlockers don't cut it.
It's a trade off. I was willing to sacrifice the ability to fully lock up the diff at times, for the torque shifting ATBs do on and off-road.
I read once that a manufacturer had a diff that had ATB type centre and was also fully lockable selectably like an air-locker. That'd be perfect if available for my Defender!
The Ashcroft built ATB replacement for the Defender centre diff retains the centre locking ability. Excellent! If ever mine needs work the Ashcroft centre ATB is going in for sure.

