Thoughts based on play-through of update (with sixth tier):
Tiers are much more competitive! First game where I tailored tenets to a strategy rather than just choosing optimal beliefs. Observe Fasts is great. It makes just that much difference early on and then scales well through the mid-game. Tier 5 is very powerful!
Personally, I would prefer that tenets manipulating terrain yields be exclusively on the early side, including T3 Seek the Earth's Bounty and Purge Idleness, T4 Gather Crops Diligently, and T5 Cultivate the Land.
While I asked for more holy sites, I'm conflicted! It's unclear to me whether they are too powerful or even if they accelerate the snowball. In my game, I didn't trade, which helped keep religious blocs distinct.
The follower thresholds did not appear to scale beyond ~225. After the Medieval Era, all the beliefs were fairly automatic in terms of having enough followers.
One problem I had was whether it was possible to switch back to a previous religious affiliation, e.g. Zoroastrianism->Taoism then back to Zoroastrianism. When I opened the religion's menu, previous religions I had chosen were greyed out.
Tying religious tenets to tech works well to pace religious development, but then it also rewards a fast tech rate, hence snowball. It occurs to me that maybe tenets need to be independent of holy sites, especially if more tenets are to be added.
On that note, some other techs that seemed candidates for tenets include the following:
Ancient:
Irrigation: role of religion in organization of river cultures.
Writing: religion as tied to impact of writing.
Classical:
Hydrology: continued religious importance of large river systems.
Imperial Power: development of state cults in emerging empires.
Medieval:
Feudalism: religious mediation of social organization.
Military Architecture: new scale of religious building.
Early Modern:
Three-Masted Ships: global expansion of missions.
Patronage: flourishing of culture under religious influence.
Industrial:
Scientific Method: sum of religious scientific contributions into the modern age.
Urban Planning: industrial transition to voting blocs, social services, cities centered on capital.
Contemporary:
Insurrection Theory: e.g. liberation theology, jihad.
Suburbs: transition to cultural lifestyle.
(Mass Entertainment): Self-explanatory.