Ofc it’s a balance issue when portuguese are basically impossible to beat once your gold run out.
That’s why I always was for limiting the feitoria to only 1, this way it can be balanced, as it could be outperformed by relics at least in the gold department.
Some time ago I made a Feitorai theorycraft where I got deeper in explanation why I chose the feitorias not to produce all the res (only food and gold) and the calculated optiminized amount of ressources to achiev a desired balanced effect.
If a player has 5 Feitorias than his military numbers will be low, that is the trade off. An advantage at the same time is that the eco is almost not raidable. So the portuguese Feitoria player is rather strong defensivly but not offensively. Giving them only food and gold would make them rather strong offensively. I would rather give them more stone and wood, so they can make more devensive buidlings. The counter to a portuguese fortress are trebs, bombard cannons and rams to destroy the buildings. With low economic numbers it can be hard for the portuguese to kill the enemy siege. The portuguese needs bombard cannons to kill the enemy siege, but with low military numbers its dificult to protect the siege. More food and gold would mean they could kill the enemy siege more easily with Cavalier.
I think it would be better to force Portuguese players more into bombard towers and Castles, that can be countered by siege well protected by superior army numbers. Rather more stone than gold. Gold is better for the offensive, where it can get imbalanced. More stone makes them rather onesidedly strong for defensive, what can be countered better.
The portuguese defensive approach with both economy and military as buildings (Feitorias and Bombard towers) is an interessting game, and I think it is balanceable. However giving them more generic strength with food and gold, could be just too strong and boring at the same time.