The counter-argument to this is that we will be receiving Outbreak, which will lighten the load that has come to entail keeping your diseases active. Wonderful! The question then begs to be asked, if it's more valuable both from a mathematical and a play-style perspective to not have two-GCD's hindering your initial threat boosts then why not simply roll the entire mechanic of diseases (IT to apply FF, PS to apply BP) into a single ability with a single debuff (Outbreak to apply <Insert Disease>)?
This would provide the following:
1) Fluidity, by lessening the strain to blow through two-three GCD's prior to actually beginning to use tanking abilities.
2) Timing, assuming they leave the Outbreak ability as is, players will want to think about when they use it lest they waste it on an unimportant unit.
3) Segregation, the disease aspect will loose a little of it's "must be active" import simply by beeing seen as a bonus when available. Which to my mind is good. The previous approach was akin to requiring 5 (now 3) Sunder Armor's to be active to Shield Slam to be functionally full-powered. Silly.
This breeds another thought, what would the consequences be of simply removing the disease-bonuses from abilities and allowing those diseases to operate distinctly as a purely damage buff available to the DK whenever he/she sees a use for them?