I know I'm late at this but I support this proposal. agree that the current Tower Guards deserve and should be the heroic unit of Gondor while the current Citadel Guards will take over the role of elite pikemen and getting shields. They could even keep the names and just swap the designs although Fountain Guards or Guardians of the White Tree sounds more fitting should they switch roles. Going by the films, we can clearly see that the Fountain Guards' design is more unique and fitting for a cream-of-the-crop type unit in Gondor's roster. Meanwhile the armor design of the Citadel Guards do not differ that much from regular Gondor infantry except for the cape and shield.
I'm not sure how the Fountain Guards would look if they were to be able to toggle between sword and spear but my guess is many players wouldn't mind. I don't think many would mind either if they lose the toggle stance and become a heroic pikemen unit but capable enough to take on basic and elite swords men (similar to the Cirith Ungol Halberdiers).