It’s not that insane you will easily be able to hit that number. 140 is just the Def cap of 490 which is 350 base +140. Some people will accidentally be above 500 just due to the abundance of it on some gear sets in latter phases.
The classic formula is mob levelx5+100, so in your case, 44x5 = 220 + 100 = 320, maybe because the mobs are higher level than you they suppress your defence in some manner? I’ve only seen people becoming immune to daze vs mobs of their own level and lower