I'm on the fence for medica II, I suspect it'll play out much the same for most content, my only concern is if it'll be fast enough to still function as is when healing up from T5 Fireballs.
I wouldn't call Cure III useful just yet, this is purely a quality of life change to make it a little more useable in a few niche situations, I'll still be using it (sparingly) in precisely the same manner as before. Not sure where you are getting the 50% cast time thing from, it's just had it's cast reduced to be in line with our other cures.
I'm not sure quite how you are working out that 2 ruin II's equate to a thunder cast though!