Difficult engineers are difficult because they're difficult just like a difficult sales executive is difficult because they're difficult. I've worked in great companies and terrible companies with great people and difficult people. The reason difficult people don't survive as long at good companies is because the organization has the breathing room to get rid of them, whereas in a chaotic mismanaged organization there's still a framing in which a difficult engineer is valuable -- because mismanaged organizations aren't considering the long term implications of difficult employees, they're focused on answering "can this person help put out our current fire?".
Difficult engineers are given far too much room to be difficult because we're seen as geniuses who just need tending to. We should show employees kindness and support them in doing their best work and growing to benefit the organization, but we should not try to fix difficult people. If you're a manager dealing with a difficult engineer, you can be sure every one of their co-workers hates them and is making their life worse.
Terminate your difficult employees, don't change the number of points allocated to a sprint.