There was nothing wrong with Bungie's aesthetics. They didn't need fixing. GEN2 MJOLNIR is butt-ugly. It's butt-ugly because it's too busy and the silhouettes are broken up and camouflaged by all the weird lines. If you're an artist at 343 and you think the "metal diaper" on the old armor looks stupid, or you think the armor is too square, you're an idiot, and I can explain why in a few seconds.
The UNSC and the Covenant have very distinctive and separate shape language. This is how you tell factions apart in sci-fi series.
When I say GDI, what do you think? Mammoth tanks. Big and square. Olive drab. White-armored spec ops. When I say Brotherhood of Nod, what immediately comes to mind? Black, sinister, beetle-like aesthetic, exposed tracks on vehicles, some real Cobra Commander shit.
Okay, now let's do the same thing for the UNSC versus the Covenant. UNSC is olive drab and square. Covenant is purple and round/triangular.
Okay, with that image in your mind,
quick, what faction is this?
"Hello, I'm violet, my backpack is triangles, my knees are circles, and my face is a pussy! They don't call it Wetwork for nothin'!"
If I had to go up against super-soldiers that looked like this IRL, I would die of laughter before anything else. Even worse, you can't immediately tell that this is even UNSC gear at all. It looks like some kind of ridiculous megacorp mascot. I cannot imagine any future military that would equip their troops with gear that looks like this. It is more decorative than functional, festooned with all kinds of bizarre curves while leaving the vitals weirdly exposed. Where is the underarm protection, preventing shrapnel from entering the lung or the heart? Where is the EOD suit-like gorget to keep them from being decapitated by a bomb blast? Where do you put spare magazines or any sort of supplies?
Compare and contrast with Reach's armor, which looked practical, nailed the series' industrial aesthetic, and was instantly recognizable as UNSC gear.
There's actually a reason for this disparity.
Shi Kai Wang was one of the main artists responsible for the aesthetic of the armor in the series, as well as Robert McLees, Eddie Smith, Marcus Lehto, Isaac Hannaford, et cetera. Their art looks like this:
Ancient sketch of MJOLNIR armor from the fucking 90s by Shi Kai Wang, later seen in 3D form in the MacWorld '99 trailer:

Master Chief in his MJOLNIR Mk. VI, by Eddie Smith:
Portrait of Master Chief by Isaac Hannaford:
Halo 4's art (and by extension, Halo 5, which mostly follows the same "nu-Halo" aesthetic) was largely masterminded by Kenneth Scott, whose previous credits include... uhh...
Before joining
Microsoft Studios, Scott previously worked as a character artist at
Ion Storm Inc. from 1996 to 1998 and as an art director at
id Software from 1998-2008, contributing to such projects as
Daikatana,
Anachronox,
Quake III Arena,
Doom 3, and
Quake 4.
[4]
Oh dear. See, this is the problem, right here. If you told me that someone who'd previously worked on Anachronox, Quake III Arena, Doom 3, Quake 4, and motherfucking Daikatana was going to be an art lead on the next Halo, you know what I would've said?
"Too fucking organic. Halo isn't Warframe or Doom. Get someone who can work with squares and industrial-looking shapes."
He was also one of the leads on Rage, for fuck's sake. This is the kind of shit he does.

We get it. You can use ZBrush to make busy, over-detailed, organic, Giger-esque shit. Yeah, really fitting for Halo.
See, all 343i would have to do to unfuck the look of the games is bring back people who know what Halo is actually supposed to look like.