Especially as it screw up one of the last thing people were regularly doing : Raiding.
That's what left at end game, and the 20th reward is the driving force behind that. FUBARING it the way they have just done just made people stop raiding...
If people stop raiding, they gets bored... if they gets bored they leave the game to play another one where they won't be bored.
Communication in that case is extremely important, as well as finding a quick and relevant solution to the problem.
In some case it looks like the counters between Heroic and Epics are inverted in other they are just wrong ( and I'm not talking of the FoT/CitW mess ).
It would have screwed some people like you gave in your example, but consider the following :
Somebody with 23 VON completion : 4 Heroics and 19 Epics.
With the split he gets a chance at 20th reward again, 4 completion after his previous 20th reward.
All in all there is no real good way to make the split, as long as the numbers in the split are right, it will screw up some, and it will advantages others.
The big problem is getting the right numbers... As proved by a lot of us in this thread their numbers are just completely wrong... In some case they come out of thin air, in other cases they have inverted heroics and epics.