Great post, really enjoyed your well thought out and knowledgeable dissection of the new outfits.The primary problem with all the seamlines is that they don't really lead anywhere. They aren't there to divide the color tones.
You have new versions of simplistic costumes with DC. The Flash, Superman. Those suits were mostly two-toned classic spandex uniforms that are now cluttered with extra linework. The problem is that with each line you add in black ink, you interrupt the flow of the costume and also the constrasting shadows. The artist will end up not doing dramatic shadow because of all the busy black lines.
The balance has been struck by Francis in the Flash, though. He eliminates the lines or uses a dark red tone to highlight them. He knows a ton of black lines ruins the costume. David Finch realized that too, which is why his Batman just has the classic suit with a new belt and armored gloves. No seamlines.
With seams, they are best used to separate color panels, or to just add depth or detail. They're fine when you have a seam down the leg or arm, or two on each side of the chest. They aren't fine when the heroes look like they're wearing Halo Spartan battle armor. Compare Burnham's New 52 Batsuit with Lee's and you can easily see how one works and one makes your eyes tired.
Armor vs spandex used to separate costumed heroes from their anti-hero vigilante counterparts. Now the vigilantes are just armored to ridiculous extremes(Deathstroke, Hawkman, Midnighter) and the heroes are more complicated looking than they need to be. You used to be able to glance at a comic character and know what they represented. Now it's harder to do.
Reverting to the old looks isn't really a great idea, but simply tweaking the new ones could be great. I think the single greatest redesign in the New 52 has been the Martian Manhunter. He isn't any busier than he needs to be and his tones and costume lines break up his design perfectly. I can look at him and immediately detect that he's of alien origin who is attempting to place himself in a super hero role on earth. He should have always looked so great. But when I glance at Superman in his armored suit, I see something that looks like a regal lord preparing for conquest. He looks too official. He looks like he's trying to intimidate us. Batman under Lee looks like a man terrified to even consider facing down a gun or a knife with the amount of silly armor he's wearing, and Batman isn't terrified of anything. Lee's Batman reads like someone who isn't confident in his abilities. He wears his Batman on the outside, which is a problem.