The Basic IdeaI believe that the current Porcupine is an ill-fitting formation for the basic spear units of Gondor and Arnor and should be replaced with the Shield Wall, which the basic swordsmen and elite infantry of both Gondor and Arnor already have.
Why Porcupine is Good for factions like Rohan and IsengardThe Porcupine is primarily for the purposes of denying the enemy the opportunity to flank the unit in question. Such a formation fits Isengard and Rohan better than Gondor and Arnor, as the open lands of Rohan provide many opportunities for cavalry to maneuver and attack that an infantry army needs to defend against. Rohan infantry must be on the defense for Isengard’s wargs while the Uruk-hai need to be prepared for the Rohirrim. If their spear infantry must have a specialized formation, then porcupine would be the ideal choice.
Why Shield Wall is better than Porcupine for GondorThe Shield Wall is used to bring one’s defensive power all in one direction to block an enemy advance. Gondor’s main opponent in the lore, Mordor, doesn’t field much cavalry but trolls instead, which are not nearly as fast (meaning it’s easy for the shield wall to turn to prevent flanking) and tend to wade into the enemy ranks.
Gondor’s defenses also tend to funnel the enemy into predetermined paths, where a shield wall with all its defensive might facing one direction would be most useful. In the films, we only really see Gondor’s soldiers fight in Osgiliath, Minas Tirith, and the Black Gate. Both Osgiliath and Minas Tirith provided predetermined avenues for enemies to strike, funneling enemies through the streets of both cities into the waiting defenders. One notable example is the wall of spearmen that met the army of Mordor at the breached gate of Minas Tirith.
The Shield Wall very heavily favors Gondor’s and Arnor’s defensive strategy: a strong and sturdy line of defenders blocking the enemy, supported by archers (and maybe trebuchets) behind the lines. It also fits the spearmen more cohesively with the other infantry (Swordsmen, Tower Guard, Guardians of Arnor), and gives the spearmen additional protection against enemy infantry and monsters.
It also fits the offensive strategy of Gondor and Arnor: a slow, unstoppable advance, which the porcupine, being a static and purely defensive formation, cannot support. Shifting to porcupine would require that advance to stop, breaking their momentum. This is a problem for Gondor and Arnor specifically because the only cavalry they can deploy to make up for the lost momentum are the expensive knights. Rohan doesn’t suffer this problem because their cheap and numerous cavalry allow them to make up for the loss of momentum in their infantry if they need to stop. Isengard can use their shield bearers to protect their infantry from cavalry and don’t need to stop their advance at all. Men in shield wall can still maintain their advance, if not the speed of their advance. Gondor players will also gain a cheaper and more mobile (but substantially weaker) version of the Tower Guard earlier in the game.
Balance ConcernsThere may be some concerns about balance, as Gondor is already a powerful faction for turtling, but I think that the vulnerability to flanking while in shield wall as opposed to porcupine, weakening an offensive march, balances out the additional armor.
Spear Wall/Syntagma - Alternative Suggestion by FilipGeorg95So, because Gondor usually refers as a "beacon" of the Man civilization in Middle-Earth ( something like real life Atlantean legacy from the Plato's writings and parts of SPQR/ Greek city states ) the best solution for their spear infantry by me should be something very similar to "Syntagma" or "Phalanx" formation where the first 2 lines will hold their spears pointed towards the enemy while the rest of the battalion will hold them above the heads and shoulders of the main line.