I like the ship in general but I would give Arnor also Rangers on foot. I actually meant that there were two units, one as replacement for knight and one for the archers or something.
Elven archers I would restrict to the Sindar.
The Teleri should get a couple of unique ships, including this early transport.
Gondor also tower guards, maybe trebuchets instead of catapults and maybe ithilien rangers (not sure about these).
I would give the Rohirrim really more than just two UU's and make most of there horse units unique and maybe restrict them in the making of advanced infantry.
Isengard should get a blend of Uruk-Hai and men units I think, but not only just one unit uruk hai.
The mumakil cannot replace the war elephant because it does not exist in the game as a normal unit. Also a UU does not have to replace a unit if we don't want to. Haradrim should also get some unique ship(s) for the corsairs and we can maybe use the boarding party system of FFH to actually be able to board ships (the Lanun in FFH2 have it).
I would give the Easterlings two chariots (one with one and one with two horses). I'm not sure about replacing horseman, can also just be a seperate unit for them (other civs cannot make them).
Angband should also get werewolves and several types of dragons (cold dragon, flying dragon, normal non-flying dragon with fire). This could be an upgrade path.
Dwarven slingers might be good as replacements for the archer for both dwarven civs.