I mean, seriously. It's not even funny.

Let's say for the sake of argument that we'll compare someone who has 100 defense (which is fairly low for Tier 3) to someone with 200 defense (the sort of defense you'd get with plate mail).
That's a difference of 100 defense, which sounds pretty big, right?
...Well, there's a catch.
I've asked on General Discussion and apparently the formula for damage (when DMG > DEF which is basically all the time) is:
damage taken = damage dealt - (defense / 2).
So with a whole 100 extra defense you take 50 less damage, which translates to a whopping 1 1/4 pips of health.

How often is taking 1 less pip of damage going to matter when you're playing on Elite??

(although the wiki says that this applies if damage dealt is 2x defense so i'm not actually sure if this is correct)

Anyway, this should probably be changed since otherwise plate armour will continue to be worthless and black kat will continue to be the absolute best.
One way this could be done would be to have the special defenses (not normal) be worth more, for example, it could be that 20 extra elemental defense against a gremlin means you take 20 less damage instead of 10 less (so it's a 1-1 thing): meaning that bringing a skelly suit to a graveyard would actually be worth it for once.

(Once again, I'm not 100% sure if my formulas / my understanding is correct, it seems a little unclear but the same basic idea that defense is meaningless still applies)