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.
Also I concluded that the single feitoria could be a unique economic strategy only available for portuguese from castle age. And the res rates would be easy to comprehend for your eco macro.
For me the biggest issue is that you can make 5+ of them which then give ressource of 4 stone miners and 10 (!!!) relics. It’s just too much of these ressources that are otherwise limited for all other civs. And for good reason, as the buildings and units that use them offer way more utilty than the trash units.
Especiially if we talk about units #### ### which only need some halb protection to tear donw entire bases from safe distance if the opponent doesn’t has units with similar range to snipe them. But also just adding in some ichamps against opponents who don’t have gold access anymore is super hard to deal with.