The players could have 72 permanent Econ total if they filled all the places to settle available, Instead it will not happen because the players need to have an army be able to attack their civ at any time for a vassal that isn't currently directly aiding the players. The mountain pass is a double edged blade, enemies can use it too.
We know where the pass is and foreign enemies don't. We might also know all the juicy ambush spots along it, and how to repairably sabotage it. I don't buy that it's as double-edged as you think.
The purpose of the pass is not to be a quick route between vassal and player? A route that should be expected to have frequent use, be obvious to those who can recognize it, be forever unthouched by any environmental effects such as erosion, and potentially be the only obvious route through the region for a long time.
I mean, we could, eventually. It'd take way longer to do that, than to get this mountain pass done. But even then, we want the mega-project, because its a Mega-Project. We like mega-projects, they do amazing things, and effect the civ that makes them forever, and increase prestige. Its all big stuff.
The vassal is only a vassal because we lack the ability to control those settlements. If we meet the (currently unknown) requirements, then the Merntir will assimilate into our nation.
Its also a great choke point, the enemy enters the pass, we can strangle them as they try to make their way through. While their forces move deeper into the pass we could also start a navel invasion and secure the northern lands, cutting them off. If we didn't have the pass, they wouldn't advance and just focus on holding what they gained.
Apparently we actually got a status out of it. Also you didn't remove Golden Age.
Rock at is at max capacity for shrines, you can't build them there.
