Unless I'm locking up the rear brakes (which I'm not at the moment, they are deliberately undersize at 10") a distribution block is just fine. It isn't the cause of the current issue.
Now if I was locking up the rears all the time I would agree with you.
BTW as an aside? My Reliant doesn't even have a valve, no rear brakes! With 75 pounds on each rear tire they would just lock up instantly. The master on that car does the left and right wheel separately.