I respect your opinion but I have to say that I don’t think so.
Feitoria cost 250G and 250S, mean that it needs at least 14 minutes per building for payback. In the other hand, villagers can pay back under 1 minute and trade carts can pay back in only 1 trip. Even if 100 stone costs over 300 gold at the market in the late game, going trading then buying stone is more efficient than generating stone by Feitoria, no mention there is still 20 populations to trade, work or fight. In 1v1 game, the value of Feitoria is already controversial, and it is impractical for me that use Feitoria in the team game.
It seems that you never play AOE3, right? It is the another good game for me.
In the late game, the stones will become more and more precious and the cost of 250S will become increasingly difficult to bear. Maybe it can bring benefits as time goes by, but most of the time after construction will be a loss. There are really rare to see Feitoria in most of Portuguese games. Even if there are the Feitoria, it is still nothing to do with the victory usually, since people know that it may be not worth it in the most occasions of the intense closely-matched game.
If Viper didn’t pay so many gold and stone for Feitoria, his fatal fast-imperial Portuguese gunpowder troops could be trained earlier and crushed the enemy earlier.