I think it's honestly better to view it through the lens of it being a game design tool moreso than a philosophical debate. If you want to emphasize player choice and freedom, playersexual. If you want to emphasize characterization and worldbuilding, set sexuality.
If you're going to incorporate dating sim components into your game, it's generally better to lean towards playersexual. Otherwise, you run into a sort of zugzwang where you can
a) lock romance options to het (e.g. Persona) and alienate queer people, even worse when you don't have a gender option which also alienates 50% of said hets, or
b) have set sexuality and allow some queer relationships with certain characters (e.g. Fire Emblem: Three Houses) but have people annoyed about the arbitrariness of it, especially when there are no characters that cannot be romanced in a heterosexual way but limited queer options.
I think there's space for set sexuality, especially in linear, narrative-driven RPGs (e.g. Final Fantasy, Undertale, Zelda). Set sexuality really works when you want to emphasize relationships between characters that the protagonist/player character is not party to (e.g. ) Furthermore, set sexuality, when there is a romance mechanic, best works when you establish a boundary between player and character.
Ultimately, it's a choice of what you want to grant to the player, as well as the distance between the player and the protagonist. If you want to let the player choose between characters to romance in the game, and that's an aspect that is a design component within the game, you're usually better off sticking to playersexual, unless you want to take a hyperrealistic angle to it. If you don't want to incorporate that aspect into your game, there's genuinely no need, stick to set sexuality. If you want to establish the protagonist as a character that exists outside of the player embodying them, lean towards set sexuality.
I honestly am just tired of romance being attached as a weird afterthought to certain RPGs. It's sterile when it's not handled with a modicum of care, and it definitely cements the whole unease-inducing 'escapist power fantasy' vibe you get in RPGs that take this approach alongside emphasizing openness. If you're gonna let me date, let me date. If not, why bother?