Invulnerable Superheroes/villains wearing armor is stupid.

[Carabas]

What kind of armour stops Kryptonite?

The armour doesn't need to stop the Krytonite, it needs to stop the follow-up to the Kryptonite.

[Jim Kelly]

A Supermobile would be a better deal--it could hoover up all the Kryptonite. And with an onboard emergency medical unit and robot surgeon, Superman would get immediate attention for his injuries.

[titanfan]

It's the power of nostalgia. She needed to do the bullets & bracelets thing in the 40's so by golly, she will do it forever, even if it doesn't make sense anymore.

Or she's the smart one. It was pointed out (in the Morrison run I think). Superman is a little bit foolish. He tanks everything, even when he could dodge--is he really sure that energy bolt isn't magical, etc.

Deflecting and dodging your opponent's attacks seems like a good strategy, even if you're invulnerable.

[Jim Kelly]

My head canon for how the bracelets work is they attract the bullets to them. So even if a bullet is going to hit Steve, it will veer toward Diana's bracelet. Wonder Woman uses the braclets to stop bullets from hitting anyone else and she is better able to neutralize their impact and dispense with them than if they hit her body (where she has no control over what happens to them when they ricochet). She's doing all this at super-speed so you don't see what's happening with the bullets--you just see the flash.

[WonderScott]

I certainly never loved Diana's eagle armor.

[Frontier]

But the thing is, no character in the DCU has proved to really be invulnerable. Not even heavy weight such as the Specter or the Anti-Monitor. All of them have been beaten at least once so having armor as an extra layer of defense isn't a bad idea.

But I think the issue is whether that armor is really acknowledged in-story as offering more protection.

Like, I may be forgetting some instances, but I don't recall New 52 Superman's armor consistently being portrayed as offering more protection or benefits then, say, the classic suit or even the Rebirth/Reborn suits.

Ditto with Batman's armors.

[The Darknight Detective]

I somehow suspect that the mainstream isn't quite ready for superhero movies where everybody is almost entirely naked with a bodypainted costume, even though it would be comics accurate.

Yeah, I'm not seeing that happening in my lifetime. What works in the comics doesn't always translate to live action (though Gal, Margot, and Amber in body paint... ).