Same quality, different content.
they're really not at all, though. the Gothic Plate's production values aren't nearly as high. the screenshots make it look absolutely terrible.
a better comparison might be the Hedge Knight Armor (http://skyrim.nexusmods.com/downloads/file.php?id=13961), which DOES have very good production values and very flattering screenshots, and is also performing very well without being sixualized at all.
a mod's success, especially for clothing and armor mods, has to do not only with the quality of the product itself but also with the quality of the presentation. both Hentai's armor and the Hedge Knight armor present themselves very well, with multiple posed screenshots showing off every angle as well as action shots showing how cool they look while doing actual game things. the Gothic Plate armor's screenshots are only there out of obligation, and lack any sort of umph or "hey you should really try this out!". it's basic marketing.
i really think Nexus's tag filtration system needs an overhaul. it's nice that i can search by tag, even if that's a pretty standard feature of every content-delivery website since like 2006, but the fact that i can't EXCLUDE specific tags is dumb. i also think the focus of tagging should be pushed into the forefront design-wise, so more people actively tag mods; maybe a tag cloud on the actual mod page that isn't tucked away in some unlabeled tab.
as much as i hate all the skimpy eroge transformation bikini armor [censored] going on (while at the same time loving the idea of turning Skyrim into some bat[censored] JRPG fantasy world with colorful clothes and poofy hats and big weapons (i'm playing with the Japanese dub right now, deal with it)) complaint without action accomplishes nothing.