Decursive, along with several healing mods, were banned when blizzard changed the APi to remove the funcionality that was used by them.

It had nothing to do with any sort of round-robin type workings, it had to do with the fact that they automated gameplay and were essentially min-bot programs created using blizzard supported tools.

What they did was let you press a single key (eg curse, heal) and then using internally programmed logic determine who needed to be healed/cursed, determined priority for who needed to be healed the most, determined appropriate rank of heal/curse to use and terminated casting if a heal/curse landed on their determined character before the cast time was completed. It took all control and thought out of the process and broke the one buttons, one action rule....that is why they got banned, not for any round-robin issues.