According to your definition, redo of healer would be seinen? Most of hentai would be seinen. Madoka magical would be seinen. Dead tube would be seinen.
If that is what it means to be seinen then a story should be tagged with something like
*) delusional
*) grounded
*) wishful thinking
*) animemind
*) realistic
People and generally people who read other medias except things from Japan expect mature stories to be well, mature. Meanwhile most of Seinen media is saturated by edgy contents. The Seinen category was initially made to separate the delusional shonen series to a grounded realistic seinen entries. Now it has become just a unregulated edgelording sausage fest.
And lastly please define a genre about constructing a media and how it targets the audience rather than what the target audience would be. It's like MLP's target audience was little girls and now mostly grown men follow it. Would MLP(My little pony) be Shoujo or Seinen?
I would honestly defer to the author themselves, as in most of the tags here for shojo/shonen/josei/seinen are determined by the magazine they are published in rather than the particular content of the story. for many in north america, Berserk is the introduction to "seinen" manga/anime which i feel is where alot of the edgelord complaints come from, but Akira is also seinen, as is monster, lone wolf and cub, MPD Psycho, blade of the immortal.
the term seinen literal "
Seinen manga (
Japanese: 青年漫画; lit. 'youth comics') is an editorial category of
Japanese comics marketed toward young adult men." the mistake many in the west have made with the definition of the term is positing it as meaning "adult mature literature" when it means targeted at 14-20 year old males, as shonen is mean to aim a 8-14 year olds.
sienen is a catch all term for manga/anime aimed at an age group. it is not a term to describe the content/genre/writing style.
if you really want to bring western media, Adventure time is a great example of media that could be argued is really sienen more than shonen if applying the japanese termimology (not that i agree with doing so).
unfortunately while i agree there is a definate overusage of egdelord tropes in manga period, i find it to prevalent across all genres but Josei (where it is present but provelent)
As i am a pedantic nerd, who really values (but fails horribly at) being accurate, i have to reiterate, when it comes to the terms shonen/shojo/seinen/josei, is the author and publishers intent. if it is published in young king ours, regardless of how edgelordy it is, that is a seinen magazine, therfor the contents should be labeled as such, where if published in shonen jump.....
also while you can write a seinen/josei story told through hentai, that doesnt mean all hentai is seinen/josei. when discussing erotica we bring in different storytelling rules and guidelines that complicate generalization.
it would be nice if there was a term different than seinen to differentiate between works written as mature literature a la 1984/slaughterhouse five/lone wolf and cub/akira and your standard YKO fare but we don't really have it, so we are stuck with the catch all that is seinen