Donjon at home: Barracks that shoots arrows when you reach feudal. (allows archery / stable)
This way opening archers is not delayed by having to wait for its construction time, sneaking on a woodline for a fwd can be effective since the first moment of feudal, etc, will become a fun civ that will do fwds or play feudal nicely!
A donjon without attack (and even worse a forward one) is just helping your opponent throw away your 175 stone with villager.
Sound good does not work. If you want to move forward with your vil to build donjon, you need early loom which means you will -1 vils also one of your vil will move forward; that mean -2 vils. Even your vil manage to build donjon: Enemy can easly rush with vils and take down. In the end you will have (average) %10 less eco and wasted 175 stone.
Root of the problem: It’s a terrible idea to make donjon a prerequisite for range/stable, the two absolute necessary opening buildings in feudal age. If you want to use this feature, you lose initiative.
Donjon should count as a prerequisite to castle age instead.
players click loom then click feudal. when player clicks loom, at the same time you send your vils forward, by the time they leave the base with the scout loom is in, then feudal age research starts. before you reach feudal, the construction starts behind the enemy woodline. you are not going to do in range of vision of the enemy. the enemy will only know about it when it starts shooting projectiles behind their woodline, the exact moment feudal is reached. at that point you can make a range right away.
you can do it home, no need to make it forward, that is just an optional feature for good players
a donjon at home is a barracks that shoots arrows once you reach feudal