Back in the day, I would just buy a new ram from a newly conquered city instead... easier that way.I vote for "yes".
Its power is at least comparable to Mongolia or Gran Columbia.
Free heavy cavalry is insane, but actually the most insane part is that "cavalry get 100% damage against walls".
This reminds me of the good old days when every domination victory is finished before T150, including those continental ones.
And this is also combined with another insane, Mongolia-like strength bonus.
What if you put Mongolia to the very vanilla version? even under that version, you need a ram for cavalries. Rams only have 2 movement, but apostles have 4 movements, and you can select the ignore terrain cost belief.
Apostles have 4 move, BUT you need to found a religion AND have a holy site, AND spend charges, so an apostle is consumed every 1-2 cities, and that really hamstrings any bonuses they have. A ram at 260 gold, doesn't scale, is far cheaper than an apostle (gets easily to 500+ per apostle once you've bought several).
I wonder whether free heavy cavalry is that insane. With production cost cards, one would wonder whether it is better to just build the unit straight up rather than finish a whole district. (what this does allow is for you to produce them beforehand and then finish them right when you unlock the civic, otherwise you just get plain chariots) There will come a point where the district becomes substantially more expensive than just chopping out the unit. Moreover, it seems this comes really late (divine right) when compared to feudalism.