I'm not sure how a gold reward for conquering is comparable to free monuments. Buy monuments with the gold you got from capturing? I'd rather have the monument up front to beeline Oligarchy while taking it out of the build orders to set up my expands, encampment, and Legion pre builds. I suspect Trajan's Legion rush will be swifter in most cases, and timing is everything. The late game gold seems negligible due to pillaging w/ raid and trade routes stretching across Rome's empire. Still, I'm excited to try out new, free content.
These are my sentiments as well.
Free monuments are very, very powerful for rushing Oligarchy, and even the Agoge card if you fancy that.
Gold from capturing cities is anti-synergistic in that gold is not really an issue at this point in the game (first early war), and if you needed gold it would be for buying units.
But those extra gold-bought units you would want to have
before you actually attack your neighbour, not after you took a few of their cities and they are about to collapse anyway.
There is also anti-synergy when playing with Barbarian Clans mode enabled.
You get gold for clearing camps and you can buy cheap units from barb camps, that's fine.
But once you clear out a camp (for that gold), the camp is gone and you can no longer buy units from it, which is awkward to say the least.
Not well designed, essentially.