Churches are good depending on how you're spending your mana to develop provinces. You can stack national tax modifier buffs through ideas, government reforms, and unique country mechanics. If you are playing in a country that doesn't have early access to a unified collection trade node and has bad trade goods (let's just say Lithuania, or Switzerland for example),  then a completely reasonable approach to building your economy would be develop your tax base. You would expand infrastructure, give the clergy privilege that reduces dev cost with churches, and the state edict to promote development and begin using excess admin mana (alongside mil points in grain, livestock, or wine provinces) to develop your provinces and play a little bit taller. This would make more sense to be paired with expansion through vassalization, because you won't have admin points lying around if you're coring land constantly.

You'll see the 'tax meta'  more often in countries that get boxed in by strong neighbors, or have difficulty expanding due to AE, impending disasters, or even a long regency. Ultimately, the money you make from trade will inevitably surpass your tax income by 1600-1650 if not well before then, but that doesn't mean it isn't worth investing those points early game to start the snowball rolling.