From 0-1250 elo ranges Port have <50% win rate, proving it is UP civ.
Now, there is what looks on a superficial level like contradicting evidence from 1250-1900+. In fact, the largest positive win rate from 50% baseline is at highest elo brackets, 1700-1900+. But to be reasonable one must look at the fact that the best player in the game, probably of all time (breeze brothers), heavily skews this % by playing port in a lot of games, including with 81% win rate on one account. Thus deducting false results coming from breeze performances, Port is actually shown to be UP at highest elo levels. And from middle elo ranged, 1250-1700, difference from 50% baseline is negligible.
Hence objectively speaking there are 3 category of results judging by win rate: (1) 0-1250 = Port UP, (2) 1250-1700 = Port balanced, (3) 1700-1900+ = Port UP. Majority of evidence weights on conclusion that Port is UP.
3 organ is not enough
Now I admit this is speculative but I propose that the main reason for why Port is UP is they cannot competitive with strong enough artillery early in the fortrtress (iii) age. As we know, cassadores are very difficult to sufficiently mass in a large enough amount due to excessive food demands on settler production + the extreme high food cost of the cassador. Thus, to compete in RI/Cannon war Port is forced to rely on cannons.
Of course, it is not usually to produce cannons early given the high cost, and thus like in many matchup the cannon shipment is integral for the balance and play considerations and potentials.
Thus I have highlighted some important facts: (a) Port is UP, (b) in general principle, cannon shipment is integrally important for balance.
Hence naturally it is the place to look for the reason for [a] (that is, why is Port UP?) in their fortress (iii) cannon shipment. Here you will notice Port has only 3 organ gun shipment as their equivalent to 2 falconet of many other civilization.
Hence, I propose for the balance consideration to be improved to make the 3 organ shipment a 4 organ gun shipment.
This should enable Port to compete more fairly on an equal basis in early fortress in many matchups and increase the balance of the game.