Upper tiers of an action (such as Fire II and Fire III) will be abolished.....

[NarikoStar]

I would love for you to actually try this on some of the current NM's, go on, go cast Cure 3 on a tank during DH dungeon Orge when the tank is 50% and watch the ogre rape your face.

Not to mention as cure gets stronger, it will likely have a higher delay, what if I dont want that delay?

I will say, with DH came out (1.18) I did not use this method so I cannot speak for then. But since 1.19 I've used this method on Ifrit, Strongholds AND Darkhold (both Ogre and Batraal & it works just fine) Of course you wouldn't do this without Soughspeak, Out of Sight and before a tank gets any of his abilities off. By the time your tank reaches 40% they should have exhausted all of their abilities once and casting a Cure III should be fine.