Basically, if you call ^that^ logic conjecture, then this logic:
OP asked a question about 20 resistance --> therefore +20 resistance=significant
is closing your eyes and taking a stab.
Regardless, I feel like I'm overexplaining myself a lot here on one small technicality… in the future don't ask me to defend my word choice (such as very insignificant).
This topic was posted for gear advice. My advice is, if you're level 100 and you've got $$, don't equip level 40 gear, and that includes Galar's set. You can get much better stuff for your level.
Your DL helm also adds 160 chaos resistance. I'm pretty sure that Necro deals chaos damage, so that would sufficiently explain the damage reduction.Now let me give you something based on my actual experience with the Necro boss in sewers. I usually have 1,354 Cold Resist. But when I wear my DL helm it adds +93 cold resist for a total of 1477 which is 93/1354 = 6.87%.
Pretty insignificant? One would think so but it is a lot of help. Instead of being hit with cold damage between 800-1200ish, I would see a drop from 600-1000. Again, although I do not have concrete data because it's impossible to keep a log of all the damage hits I receive, my perception is that wearing the DL helm, even if it's only a slight upgrade to cold resistance, reduces damage by a LOT.
And, depending on the helm you would have equipped otherwise, it could enable the Dragonlord Aura set bonus, which grants +800 chaos resistance on top of that.