It's about both really. I believe it's equally important to list out both the positions of the characters (MC and anyone you can have sex with specifically) as well as the kinks of the game. I put more emphasis on defining whether a game has top, verse, or bottom content because a lot of the erotic games I've played tend to be more or less vanilla with very few kinks. On the other hand, anal sex is almost unavoidable in erotic gay games, even though some people think that shouldn't be the case, therefore the MC is either going to bottom, top, or both. So most advice saying to list out the characters' positions (and who you can have sex with) would be more important than saying to list out all the kinks in the game for most gay erotic creators. Also while I do advocate for kinks being optional, up to and including making every sex scene skippable, that's not what this article is about. If a creator wants to make a kink a thing the player has to do, I'm not going to oppose that, but I would tell them to warn them that such a thing happens before that happens.
Yeah, my game is on the contrary, very heavy on non-vanilla kinks, I should have mentioned that. That's why I placed so much emphasis on the kink listing, and ways to warn or avoid them.
But positions? honestly, when I play NSFW games I don't even care if the player is top or bottom, I just go with whatever content the game has (there so few of gay games, and even less bara games. Refusing to play a game because it has only bottom/top content doesn't work for me) and I don't even question myself about that, I enjoy both content. Unless the game throws me a kink that I don't like, that's where I start questioning. But positions? I never did.
Maybe my mistake is thinking that everyone is like me. I'm still not sure how to avoid this problem on my game. A comprehensive listing of each character is a no-no, my game is text based sandbox, it has many characters already and with each update the list grows exponentially. I see that this can work on VN that has a handful of characters with CGs.
And putting a big, red warning at the game? If I say my game have only bottom content is a lie. There is top content there. So I'm not sure how to proceed.
I can't say I have a perfect solution for you, I will admit for your situation specifically it's hard. If I were you, I'd just say "This game focuses on bottom content, but there is a good amount of top content in it as well. There are some characters in the game who can only top regardless of the position you picked. There are no plans to add scenes for them to the bottom." on the itch.io page. If you can, maybe list out all the total tops (and total bottoms if you have any) in a document that the itch.io page has a link to. An option that warns which characters are total tops (or total bottoms if any) as soon as you meet them would be nice, but maybe that's too complicated.
I like your suggestion. I'll update the FAQ section of my page and I'll consider making an external spreadsheet or something listing who's a top, bottom or versatile. I still think is kinda spoilery, but if you're warned before going there, I guess it's alright.
The warning as soon as the player meets them... I don't think I'll implement it in my current project. It's kinda like spoiling that this character will have sex with you (I still consider fun to discover that character might have, or not, sex with you. For some characters is pretty clear, for others it isn't), and I'm on a point in the development that is not possible (well, it could be. but doing that for every character would take weeks, and I can't afford that), but it's definitely something to consider when I start my second project, who knows. I'm not closed to that suggestion either.
It's good to have these discussions, there can be solutions for each case, even in complicated ones like mine.
I'm still not sold on Top/Bottom / Dom / Sub should be listed, TBH, I don't like how people stereotype "Dominant Top" or "Submissive Bottom", IMO it's too cliché and over-used. That's why "Small on Top" is high on my list (but it kinda goes to the opposite extreme XD)
But I like your idea of an "External documents" that list all the characters and their positions (or at least some hints). So people want can look into, others don't need to worry about being spoiled. IIRC, most Japanese games have this feature. And this will be more useful for WIPs and their backers.
There are few games even have a brief "Official walk-through" (For free, not those sell for more than the game itself), goes into more details about things you might wonder.