When making a group of players for your RPGs you want people you like playing with, and you want people who will contribute creatively. The first is more important than the second. Honestly, I think that’s true in nearly any group you’re part of; you’d best be able to get along with them if you’re going to spend so much time together. If you’re spending time together for fun, that’s doubly true. I don’t mean there can’t be friction, but I do mean that you should feel comfortable with them, able to ask for what you want and have them honor those requests and talk with you about it.
Those two factors—whether you like spending time with someone, and whether that someone contributes creatively—aren’t entirely separate from each other. Someone that you like playing with, and who likes playing with you, will have an easier time falling into a collaborative creative rhythm over time. Someone who contributes creatively is likely to add things to your game that make it better, and which make playing with them more fun. But.
I don’t think it matters how much creative material someone adds to your game / story / group if they are not fun to play with or be around. Spending time with someone who contributes creatively while being fundamentally not fun to be around is honestly miserable. If they keep adding new ideas but can’t play well with others, or if they aren’t willing to engage with your time together *as play,* you have a recipe for trouble. When I’ve faced this before, I’ve felt stuck: the player’s contributions are excellent, and feel good, but I’m constantly reminded that the player themselves is just not quite right as a fit for the group.
Without outside requirements to include a negative player, there’s no reason to keep them. Until something changes, their creative contributions aren’t worth the added stress of working around their presence. That doesn’t mean that people can’t change, but it helps to have a certain level of shared trust and context before encouraging someone to shift their way of being in a group. Whether you want to put in the work to help them change their behavior is entirely up to you, and that work is *not* required of you. In the long run it may be helpful for them if you tell them why you don’t want to play with them, but you don’t have to engage in that potential drama if you don’t want to.
Relatedly, paying attention to how other people in your group feel about each other is worthwhile. Your experience, obviously, isn’t the only one in your group. If someone in your group is making another person miserable, that should be resolved too.
Also, just because you like spending time with someone in other situations doesn’t mean that they’ll necessarily be a good match to play RPGs with. It helps, but it’s no guarantee.