Difference in view points. I don't view any of the situations you listed (except maybe the resisted mezzes) as situations I would use a mitigation disc for survival. Those situations are an evasive style disc, not a mitigation disc.
Where we disagree, is reliability. If we go by your 30 second standard, every time I click my disc, I am getting more out of it now than I will post change. Many people are. Every one of them stands to lose something. 5 mobs dishing out 30k unmitigated damage means 1 thing... that 3kac tank has to have as many or more hps than I do just to survive the 22500 hit of damage. That does not include procs, aes, and other random spells cast by mobs within Tier 3+. Regardless of all the survival tools in the world, short of an evasive disc, the tank is dead.
I've used this disc generally dealing with Squires in Crystallos, and named across Tier 3. All of these mobs have the potential to two round me out right, which has happened with a shield up, aoti running and decorum rk2 still burning. Can't really say that I am using my abilities on mobs beneath my gear. I use it any boss mob that I am engaged on, be it Mayong, ZiT, AyoRo, or even FC progression.
I am not willing to give up on the 1 min duration. Some stand to gain 1-2 ticks, some stand to stay about even, and others stand to lose 1-5 ticks worth of duration off of every use of their disc. That is not a "win-win" situation to me. That is a direct nerf to a disc that lasts it's full duration for me, consistently. I lose up to half of it's effectiveness. There are others like me out there, whom would be in the exact same boat.
However, if the cap was removed, and the duration stayed the same, I wouldn't utter one single complaint.