Pre-re formula was (SDEF + HDEF ) /100. You were looking at Renewal formula.
Since HDEF was removed from calculations as part of a change here, its actually only [SDEF/100] here.
So say a mob with 140 vit, you would deal floor[140/100] = 1.4x Damage. Note that Thanatos makes your damage fluctuate a lot more so its harder to actually test.
//Time to disappear again