I think this spec's evaluation is giving a correct, but ultimately unhelpful, number of possible Kill Command casts under Cast Efficiency.
The number of possible casts seems to be calculated as simply ((fightLength / hastedCooldown) + numBestialWrathResets). That should be approximately correct.
However, the priority list for the spec, according to Icy Veins, lists Dire Beast as a higher priority. Both abilities are on the GCD, and their short cooldowns (12s and 7.5s) ensure that they collide with some frequency.
Therefore, even in ideal play, it is expected that Kill Command be delayed for 1 GCD with some regularity. Consider, for example, this log. Odipus holds the second-highest ranking for their iLvl bracket, and maxed their efficiency for all other cooldowns, but is told "can be improved" because they only used 56/75 of the maximum possible Kill Commands.