While I don’t go so far as to say it ruins the game, I do believe the Cumans economy bonus should have a better conception and that it’s still an obstacle to AoE II DE leaving a long-lived legacy of being a prime example of good competitive balance, like a Starcraft 1. Same thing for Feudal Age Siege Workshops and Castle Age Capped Rams.
It’s one of those things where the abundance of choice ironically removes choice by having one option that’s clearly superior vs. everything else, like the Double Castle Arambai vs. all the other great Burmese options no one uses because Double Castle Arambai is clearly almost always the better option.
Although this is straight from AoE III, I think the idea is so much better than a 2nd Feudal Age TC that I wouldn’t mind an exception for AoE III mechanics in AoE II. Which is for the Cumans to have a unique Villager unit that gathers faster than other Villagers and has stronger starting stats. But it costs more food, creates slower, and is more vulnerable than normal Villagers to either melee or ranged attacks (i.e. starts with 40 HP and 1 melee armor but Cumans don’t get Loom?)
This way I imagine the Cumans would play like they do now with a bigger initial economy investment that grows into a very strong early Castle Age. But now they also have a reason to play a standard Feudal Age.
To me, those are more like bending the rules every civ has rather than breaking them and becoming their own rule like the Cuman bonuses. Even something like Khmer bybassing building requirements is still bending the rules to me because the military and conquest portion of the game necessitates making anyway at least some of the buildings you can skip.
Portuguese are the civ that receives free TC in each age in AoE3. But to balance it off, in AoE3 vills are 2x the cost of vills from AoE2. Also, you can spawn a lot of army (pikes/musks) to just rip off the second TC in Commerce Age (Feudal Age - Age II for AoE2).
Now in AoE2, coming to the point, if going to castle age is the only way to counter it, it definitely is a bad design let alone if it is broken or not.
You are seriously diminishing the early pressure portion of the game. OFC the cumans are going to out boom you if you do nothing until Imperial.
Those vills cost food still, working from 2 tc’s costs food that you could spend on other upgrades, units etc. If their eco is raided or the boom punished, they will be in a pretty rough spot.
Also the essence of Age of Empires isn’t necessarily only the civ advantages/disadvantages. It is so much more. Having 2 tc’s isn’t game breaking or insane, the only thing is that you percieve it as such.