Well I can't speak for anyone but myself, but I don't find the 'spinoff' term offensive in this case, but rather a mischaracterization of (at least some) these non-numbered games. Just as you described, people hear 'spinoff' and they then assume things about those games that may very well not be true. Leading some to skip out on playing them.
If you want a recent example, someone made a topic asking in which order they should play the mainline FF games in, and said they're skipping the spin offs.
Final Fantasy Tactics is not a numbered game, but should imo by no means be skipped if your concern with spinoff is quality. In fact there are several numbered games you should sooner skip, if that is your concern.
When you mention Mario Bros as an example, it's disregarding what this conversation is about.
No one questions or cares whether Mario is a spinoff or not, because Mario Bros is a franchise of its own, fully enjoyable without playing or knowing about Donkey Kong.
That is not the case for the non-numbered KH games.
Though aside from the fact that whoever wrote that wiki portion didn't establish why those KH games were supposedly spinoffs, and got the number of handheld games wrong (said there were 4, but there are 5), if I look at the definition above, it's vague enough that it sounds like it could be applied in the same manner to Kingdom Hearts 2 & 3 as well.
That's why I wanted to hear from you, in your own words, why you think Birth By Sleep should be referred to as a spinoff, by whatever definition you use, rather than just hearing what that definition is. How it differs from KH2 and 3 to the point where it's more proper to call it a spinoff.
And please, use the examples from my previous post in your response, if you could.
Although I understand that you consider its story just as important to the the series, which was the main point I focused on. It's the foundation for the main plot in KH3. Similar to how KH 1 was to KH 2.
But that's also why I don't quite understand what it is about it that makes you categorize it a spinnoff. It shouldn't be the gameplay. There's an argument to be made for Chain of Memories since its combat differs quite a bit from the rest of the series, but I believe the things they have in common outweigh what they don't.
I don't think the same can be said for Mario Kart for example, since the entire premise of the game is different. They could re-skin the characters to something else and change the world, and no one would have suspected it was based on Mario or Donkey Kong.
Re-skin BBS and you're still very much playing a Kingdom Hearts game and experiencing a KH story.
When it comes to a series with a continuous expansive main story, I don't think I can consider it a spinoff unless other aspects of it that are at least equally important, are vastly different.
Persona 4 Arena for example is a spinoff in every way. Not only is the gameplay completely different (it's a fighting game) but the story in it is a stand alone side story, largely irrelevant to the plot in Persona 4. The Persona 4 story is also complete without having to play P4 Arena.
And again, I find that none of these things are true in the Kingdom Hearts series.
What I do think is that some people first assume that the non-numbered KH games are spinoffs because of what Square decided to put on the box cover, and then when asked why they think so, rationalize it in ways that, at least so far to me, has not made much sense. That's why I want to hear your take.
Just an aside, I mentioned Mario because it was a glaring example of something that is a spinoff, but is well regarded. Spinoffs can become well regarded series in their own rights, but don't have to.
The Wikipedia page is actually right. There are 4 games between Kingdom Hearts 2 and Kingdom Hearts 3. There's a 5th one, Chain of Memories, between KH1 and KH2. The article merely says "notably" between 2 and 3, presumably because the one game in between KH1 and KH2 is not as glaring an example of spinoffs as the 4 handhelds and 1 smartphone game between KH2 and KH3. But that's being nitpicky. The point is I agree with it's definition. A piece of media, including video games (which KH is), derived from an already existing work (which the handhelds are of the numbered games), that focus on more details and different aspects from the original work (which each handheld title does). And the article author does establish why they're spinoffs. He says they "expanded on the original thread of the story". The original story of the numbered games focuses on Sora and friends and their battle against the main antagonist of the series. The handheld games tell about events outside of that or focus on different characters, while the numbered games continue that main story thread. Yes, the main story thread references details from those other threads, but they are still other threads, not the main story thread. In other words, In between each numbered game, there have been many games, and I like them, but I was always looking forward to the continuation of the main story thread.
And that's why this discussion about what term to refer to them by misses my main, original point. Are they spinoffs? Maybe, maybe not, I really don't care at this point. That is the word I choose to call them by, and no one will change my mind on that, but if you'd rather not call them that because you have a different understanding of what a spinoff is, that's your call. My point has nothing to do with them being spinoffs. My original statement was:
"It did take them 13 years to make the next mainline game. Spinoffs don't count. I love Kingdom Hearts, but SE really dragged this whole saga out way too long, and I'm still mad at them for it. And I don't hate the spinoffs either. 358/2 Days holds a special place for me. But damn, KH2->KH3 13 years? Come on SE. Not cool."
People were very upset that I called the non-numbered games spinoffs. But that's not the point. The sentence after that is the point: "SE really dragged this whole saga out way too long, and I'm still mad at them for it." If you don't want to call them spinoffs, that's fine, but even though they contain important elements for understanding the story of 3, they still aren't 3, they're something else, and they're not what I was waiting for in between 2 and 3. I knew 3 would be a continuation of Sora's main quest, and that's what I wanted to see. BBS isn't a continuation of Sora's main quest, it's a further complication of the plot, on a system I don't own and don't have money to buy. That was my perspective when it came out. I just saw BBS as an annoyance because I wanted to see Sora's story continue, and I didn't want to have to buy 5 games and 4 handheld systems to understand it. That frustrates me. I'm frustrated with how they choose to present the story. I'd rather they just made 1, 2, and 3, and presented them in such a way so they could be understood by playing them in that order. KH2 could start by explaining briefly what happened in between 1 and 2, and maybe sometime later they could make a game that expanded on those details, but I'd rather it not be required to play to understand Sora's main struggle against the main villain. Prequel games can be interesting, but I'd rather they add further context to a plot I already understand, not interrupt a story I want to finish and force me to play that first so that I can understand a sequel. Can you not imagine how that might be frustrating to someone? So call them spinoffs or not, but the focus of those games is on things that are interesting, but not the same focus as the numbered series, and the focus of the numbered series is the plot thread I wanted to finish, and that I waited 13 years for.
TL;DR the point isn't what you call the non-numbered games or whether their stories are skippable, it's that the focus of the numbered games was on a particular plot thread and I wish that Square Enix had finished that plot thread quickly in a way that could be understood sequentially without needing to play prequels or midquels or games that expand the plot into other winding threads that add important details but don't really move the original plot forward. Instead they paused the plot thread I cared about for 13 years to make games that just complicated the plot. Now again, some of those games were good, but they still sidetracked from the original plot thread I wanted to see the finish of.