My view is not that Diogenes Laertius is misleading but, as Don and Kalosyni have stated recently, that eudaimonia is not "happiness" but instead "(an enduring sense of) mental well-being."
So then the problem is in fact in the tendency of most all translators to use "happiness."
But Cosma Raimondi, depending on the Latin he is using, is not seeing the need to explain this terminology either, and everyone who reads these descriptions of happiness is totally afloat in a sea of ambiguity as to what is really being discussed, because I would agree with Cosma Raimondi that while in the process of being roasted I would not be feeling an "enduring sense of mental well-being" at that moment either.
I think we have a lot more to do to communicate the relationship between the feelings at any particular moment vs a term that appears to subjectively evaluate a conceptual sum of total experiences past, present, and future.
"Blessed" would probably still need much more explanation, but would seem less off-base to me at this point, because again, the issue that is being described is going to be something that may indeed apply in some way, but which is not going to prevent us from crying out in pain while we're undergoing the experience of the moment.
The whole ball game here is communicating the relationship between this evaluative term, whatever it is, and the pleasures and pains of the particular moment.
And I, for one, would not want to volunteer to undergo the wrack as an experiment to figure it out in real time! At this point I am much more comfortable taking an inventory of all my mental and bodily pleasures and pains at any particular moment and doing the best I can to maximize the pleasure and minimize the pain.
Then if some philosopher wants to tell me that they have a different point to make when they are discussing the term "happiness," I will smile and nod and find it enjoyable to hear the discussion, but not for a moment accept that their evaluation overrides my own feelings.