I know only one sentence about Ali. However, going off that and the little I know about the Caliphate, I think the early consolidation of power by someone who has some semi-plausible claim to divine right would give a huge boost to the caliph's power. IOTL, weren't the imams and jurists the primary interpreters of the Quran, and the Caliph at least theoretically supposed to listen to them? But, I also recall that one early Caliph compiled an official text for the Quran and burned all divergent copies - so perhaps the office's power could fall even despite Ali's claim to divine right.
Thoughts? Am I totally misunderstanding things iOTL?