If you're simulating, be sure you're not overlooking the 'opportunity cost' of working on the next-valid-block when you're 'holding back' blocks.
Example:
Cartel finds block N. Instead of releasing it right away, Cartel holds it and starts working on block N+1 (trying to get a head start).
Before Cartel finds block N+1, somebody else finds an alternate block N and announces it.
IF Cartel loses the race to announce, then Cartel has wasted time looking for a block N+1 that will not be accepted.
If they simply announce block N right away, they'll never waste time trying to find a block N+1 that has only a 50% chance of being accepted.
Unless the Cartel can propagate their blocks across the network faster than the whole rest of the network, there is never an advantage to holding back blocks.