Is it impossible to convert Mecca as Persia? I have +3 stability, a missionary, completed religious ideas and 100% piety.
This sums up to 11.51% missionary strength. Mecca requires at least 12% missionary strength.
Build fort level 5 or even 6 and hire an inquisitor.
Even Buddhist, which gets no max piety bonus, can get this:
2% decisions (monastic education, anti-Christian edict)
2% base
3% divine supremacy
1.5% stability
2% inquisitor
.6% fort level 6 (at this point, you're swimming in money, so if you're going to be ahead of years in miltech it's not a big investment).
This sums up to 11.1%, not quite enough. But Muslim?
2% base
3% piety
3% divine supremacy
1.5% stab
2% inquisitor
1% decision based on leader
.6% fort level
That's 13.1%. Hard, but it'll chew through Mecca. At least it's POSSIBLE for that religion. This is before events like religious temp 1% or "increased narrow-minded" in innovative and such, which can push you a little more still.