What is the importance of high defense in melee?

Let's say going from 40k to 50k, what would be the benefits of it?

Consider other stats are covered, such as high life / ar / dmg.

Ty

absolute numbers depend on your opponent's ar:
chance to hit = 2*alvl/(alvl+dlvl)*ar/(ar+def)
plug in the numbers and see if chance to hit decreases in a remarkable way if you enhance your defense

example:
assume you are on the same lvl as attacker, attacker has 25k ar, you have 30k def. chance to hit: 45%
25k ar vs 40k def: 38%, which is a noticeable difference (you take about 15% fewer hits)

Good explanation. Ty