Well, the main question is how much you value your AP.
If the answer is "a lot", then you should hit the most rewarding dungeons regardless of health loss, just for that extra experience and the chance for good items. Isolde, you got unlucky for a bit, but note that when they drop items, enemies always drop items
of their level. That means that in the earlier dungeons you'll get maximum level 6 items, but in the new ones, if you're lucky to get some items, they can be up to level 9 items.
EDIT: It's also worth noting that you lose 1 durability per raid regardless of its difficulty. This, too, makes less rewarding dungeons less profitable in comparison to high-yield ones.
I'm only level 6 now, but I definitely want to try out the newer dungeons