Lightning Resist Not Working On Gemling Legionaire During Act 2 Final Boss Fight

Hi,

During the last boss fight in act 2 my lightning resist on my Gemling Legionaire seems to not be working properly or the boss is overtuned. My lightning resist is at 65% and one lightning spear takes out almost half of my health. Not sure if this is normal and I just need to get gud or there is something wrong. I can beat the act 2 final boss on my other builds just not this one. My other builds do not seem to take as much damage.