Ah, in humankind, it is so easy to convert to a new religion !

We just need to have a territory with a 10 % faith for a foreign religion and by magic, we convert all our empire.

Conversion is a mechanic that allow a player who has done nothing, who hasn't played religion at all to get free access to very nice tenets and steal the hardwork of other players.

Their is only 2 negative consequences to a conversion :

-the stability is said to fall during the reformation, I say "is said to" because I actually noticed that sometimes, instead of falling, the stability rised during a reformation ! I don't understand why.

Anyway, stability is something that has a limited impact in a lot of situation, if the stability was high before the reformation, it will not have time to fall enough before having a real impact. So that, if this malus worked always as a malus, this is not that much significant anyway

-Accepting a reformation means having less holy sites, which means less impact of the compatibility if the civic is taken, but 1 % science in each of them is not the more impactful thing in the game, for example, a scientific agreement, that is 5 % !

There is a lot of advantages to reform our religion :

-as already pointed out, get free access to nice tenets without having put energy in the religion aspect

-avoiding grievances

-avoiding to face teutonic kinghts at their full potential if the case arises

-getting access as much as the player who has a strong religion to influence bonus per territory if the choice "open-minded" has been done in the religious tolerance civic

The current system of religion in humankind is really unfair and does not make sense at all in my opinion.

However the base is good. The base is excellent. But it just need to be fair to be a nice gameplay. I like a lot to see how the faith is spreading in territories, all of that is great !

Converting it in a mechanic really interesting is really simple, and need just one thing :

-inserting a major penalty for the player who converts.

That's why I would suggest to make of reformation something similar but in a lesser extent to a revolution.

For a few turns, the player would lose -10 % of all FIMS in all the cities, even if the conversion has been obtained by war or by a grievance accepted. I think however an exception could be thought for the conversion of an ally which would be the only case to avoid the -10 % FIMS.

In that way, the player will have a real interest in asking a conversion of his neighbour : he will disrupt his progress. 

They could also make the founder of the faith gain more bonuses if someone else adopts their faith. Maybe even adopt the CIV mechanic of having founder-exclusive tenets.