We are not talking about a need situation though, we're talking about dungeon pulls in this thread, its common sense that you need to stack cooldowns to survive a large hit, however we are talking about prolonged damage within a dungeon context, so you will be getting diminishing returns on your stacking of cooldowns, as its about taking the least damage possible, which you achieve by spreading out your cooldowns. So in this case using your cooldowns spread did decrease the total amount of damage recieved, hence diminishing returns on stacking cooldowns. If you absolutely needed to stack the cooldowns to live it would not be a diminishing return, as you would be dead, but we are talking about dungeons here. Thats why my example wasnt flawed as I was talking within the context of the thread and the discussion being had, if we were talking about surviving tank busters would absolutely be talking about stacking cooldowns.
I think that broadly we are talking about different definitions here. Im taking diminishing returns to be that you put more in at one point and got less total out of it than using less spread out, this applies to both dungeons and some of the good raid design where tanks are taking more frequent high damage. Youre taking a purely mathematical view of diminishing returns, which while valid does not adhere to the reality of the game design due to to how spikey damage is (popping more than necessary for a tank bust essentially wastes mitigation that could be applied elsewhere ect).
Ps. Auroa isnt bad fite me