I imagine this is subjective to playstyle, but I've been trying to figure out specifically how valuable the 50 resists below 50% health are in terms of clutch protection.

I generally like my blademaster sets with some form of comfy sharpness management so these two options are incidental to my resulting builds after I build for my preferred balance of damage and sharpness. Full Dragonheart really isn't my thing so I only ever go for 2 if I want it. And when presented with build options of similar defense, I've always skewed towards the ones with negative resistances that don't break -10.

Do the increase in resistances at 50% health have any value in terms of clutch survival over just having my defense sit close to ~500?

EDIT:

PS Sometimes the option of Defense Boost 3 Dragonheart 1 come up, too. But at that point Dragonheart is just a bonus from whatever single Valstrax piece I have on there, which is normal anyway.