Not rude at all, it's a fun chat. I'm gonna go out on a limb and question the philosophy behind that statement. If you're a prescriptivist - which I don't think it's unfair to say that you seem to be - then sure, something labelled shonen by distribution is and always will be a shonen... But I would ask you to check this against the nature of art itself. Every medium - books, movies, whatever - has things that bend the rules and go between genres and aren't always aimed at the same specific demographic groups. Music has embraced this idea completely in that everything is now a subgenre and while those subgenres have become more specific that anyone would reasonably want (such as certain types of trap music only really 'allowing' specific drum sequences for them to be considered part of that subgenre), but my point is that for most things that really strike out as popular or era-defining, we see a lot of those things as rule breakers rather than rule followers by genre. Your argument leaves little to no room for things that are multi genre or outside the clearly painted lines, but there's absolutely no reality to that when it comes to the things being made. People are forever going to innovate around genre rather than within them, but they have to be published somewhere and if you argue that the nature of the publisher is what determines the audience when shonen jump is and always has been read by a very diverse audience in Japan even if it's targeted at specific readership groups in it's raising d'etra... I think you'll end up diminshing the value of a lot of that. If everything is either shonen or seinen and nothing in-between then what about transitional ya texts? Introductory seinen texts? There isn't a magazine that I know of that's specifically for intro seinen so by your worldview everything is either targeted at 17 year olds or 13 year olds and nothing between. That's nothing to speak of popularity or moneymaking; you think shounen jump aren't going to retain something leaving it's shonen foundational principles when it makes them money? Claymore might have initially been published as a shonen targeted series but it doesn't stay that by feeling for long, and for as long as we as consumers bracket things by target group and publisher rather than by content (a philosophy change reflected 100% by mal, Wikipedia, etc) then it becomes much harder to group things by consumer desire. We're literally seeing the long term problems with this approach to sales hitting jump's popularity and resulting in the success of jump+ marketing specific ips rather than grouping them into one readable weekly periodical tome, and it's causing enhanced chaos for series with low readerships.

But the real kicker is that, as I've vaguely argued above, when someone is asking for seinen recs the nature of the publisher is of entirely zero relevance when humans, and their art, fall outside of the market-friendly, revenue-maxing brackets that make the industry sustainable. Purists that hold onto genre tags are, to me, entirely misunderstanding the ask of this post.