#I'm unsure if 5e retconned this more

[sky-kiss]

Succubi and Incubi only defected from the Abyss to the Hells like. 20/30 years prior to the events of BG3. Before that point, both species were considered demons and sworn enemies of devils/hell.

Now, that sounds silly but. Do consider.

We don't know how long Haarlep has been in Raphael's service, but it's certainly longer than 20/30 years. Most likely, Haarlep was a gift from centuries to millenia prior. And while succubi/incubi are more tolerated than other demons, there is still an associated stigma.

In other words, Mephistopheles didn't just give his son a sex slave. He gave him an enemy of the Hells. He gave him something inherently shameful. Something that would directly harm any of Raphael's future bids for power. Can't have Raphael in charge, his long term consort is one of our sworn enemies. And since Raphael couldn't get RID of daddy's spy, it's a good explanation for some of the irritation between the two of them.