#1 Worst: The Wild Card Rule
Before the draft took place and the two rosters were separated, there used to be something called the Wild Card rule that completely undermined the brand split and how! Superstars from RAW could show up on SmackDown and vice versa, and as a result of the same, a lot of the roster did not get any TV time at all.
The whole point of two rosters has been to give every one of the brands its own unique flavor and identity. There's so much WWE content that one has to watch during the week, that unless the brands feel different, the casual fan may just tune out.
Corey Graves deleted his Tweet! More details HERE.
Thankfully Vince McMahon's Wild Card rule came to an end when SmackDown moved to FOX and the rosters have been distinct since. I think I speak for everyone in the WWE Universe when I say that nobody misses the rule.