The faction mechanic for a claim is cheese on its own, usually it to double king is even worse. I tried William to have a decent power base against an eventual Aztec invasion, the plot to give me a claim on France went through before I had enough war score to take England so I made a faction for myself that filled up almost immediately. Presented my ultimatum expecting a war and he just handed it over. England's cooked soon after and bam I'm the largest realm (unless the HRE was still bigger, but they were fighting an independence war when I checked)
Kinda left a bad aftertaste.
Kinda left a bad aftertaste.