There are two main reasons that game genres are such a mess. The first, which seems to be slightly better known, is that categories are hard. But the second reason, which is both more important and less understood, is this:
A game’s genre label isn’t really about that game. It’s about every other game.
Genre labels are shorthand used for setting expectations. They convey what sort of experience a game provides by invoking a shared reference point. Claiming that a game belongs to a certain genre is a statement that the game is, in important ways, similar to other games in that genre and different from other games outside that genre. Therefore, the most useful genre label for a game depends completely on which other games do and do not have that label.
Suppose Apex Legends had come out in 1994. The exact same game, played the exact same way. It would have been called a “DOOM clone”. That would have been the most useful label at the time. But since it instead came out in 2019, into a world that had seen Team Fortress 2, Overwatch, Battleborn, and so on, it was more useful to call it a “hero shooter”. The only difference was which other games people were familiar with.
The best-known example of someone trying to push this in the other direction is of course Hideo Kojima referring to Death Stranding as the first “strand game” when nobody knows what that means. This completely fails to clarify what kind of experience the game provides. But who knows; maybe in a few years “strand” will be a widely-understood genre label.
It’s expected for the set of commonly-used genre labels and their meanings to shift over time, and for this to accelerate as more games are created more rapidly. And on top of that, the more games come out, the smaller the percentage of them that even the experts can possibly be familiar with.
I don’t really play shmups so it is not particularly useful to me to distinguish between their subtypes. For my purposes, a bullet hell game and a trance shooter game are in the same genre. I literally didn’t even know that “trance shooter” was considered a shmup subtype until I looked it up just now, even though one of the listed examples is Super Stardust HD which is one of my favorites! But of course, to people who care a lot about these particular types of games, the distinctions are significant and having the subgenre labels is quite useful.
Add this all together, and what we have is: genre labels are hard to define, shift over time, and mean different things to different people. This is fine. The goal of a genre label is to compare a game to the constantly-shifting reference points around it; of course it will also be constantly shifting. Trying to “fix” this by getting super-technical and specific with your definition is like trying to plant a flag in the ocean.
(Naturally all this applies to genres in all kinds of media, and a lot of other categories too.)
