The manga Hakoiri is a hentai, not an ecchi. Anybody that read it and knows the difference could tell but it's locked from editing for some reason. It has graphic explicit sex every chapter and seems to be focused on sex instead of plot. Am I missing the difference?

https://www.mangaupdates.com/series.html?id=14298

Young Champion Retsu is a Seinen mag. The sex comics spin-off from Young Champion. Young Animal also has such a spin-off. Some publishers simply want to release porn without it being porn. Shit like this is the result.
Ecchi & Mature are bogus but this is Adult and Seinen due to Hentai being a publication form. Never a genre.

Josei and Seinen = All Ages. Hentai = Age Restricted. Aka R18.

I also read EU/US comics and am a librarian.
Manga-Masters, My ANN-Lists + Imdb

So the only thing that separates this from a hentai label is that it somehow got around some loophole to avoid an R18? I have a hard time seeing how this is anything other than hardcore porn/hentai. Ignoring the MU way of labeling things for one minute, this manga focuses more on sex than Velvet Kiss, which was considered "softcore"(ソフトエッチコミック) when the mag it was published in was still in business, never had an R18 designation, and was never designed exclusively for adults, according to the publisher anyway. Yet it sits there with a hentai label when it's less pornographic in terms of how the porn is used.

But it's not my website, I'm only a user so bitchin' about technicalities aren't going to accomplish anything apparently.

This isn't an MU technicality, it's an industry technicality. Stuff like Shounen, Shoujo, Seinen, Josei, Kodomo, Hentai, etc. depend purely on the magazine it's being published in; these aren't subjective, value-category judgments. There are definitely some iffiness involved sometime, as has been discussed before on MU, particularly with magazines that don't publicize their target demographics, but overall, this is how the manga industry functions, and it helps a lot in standardizing tagging, so that's how it is.