I don’t know about the specific situation you are talking about, but this sounds like a perfectly fine request. Needing to spent time debugging your mod at random because an unexpected patch just dropped and players suddenly can’t use it anymore doesn’t sound fun. Especially considering how little extra work it would take the studio to document their fix to the mod community a bit early.
I don’t see what you find cringy or entitled from this open letter, they explain the problems they encounter while working on mods and explain how Larian can help with that. This is the best way to handle such a request as a group.
And no, they aren’t entitled to their demands, but that doesn’t mean that those demands aren’t admissible. While they do not own the game itself, they do contribute to it’s success and the studio will benefit from helping them.
Also, it seems like you view modding as just some small tweaks for the fun of it (which might be the case for bg3, but from the letter it doesn’t seem so), but some game mods can become fairly huge, both in work size and popularity. While I don’t know much about the bg3 scene, I remember quite a few minecraft modders who received death threats because they “took too long” to update their mods to the latest version. There’s a real pressure behind that work, you can’t just brush it off because “they don’t own the game”