Well, here's my vision of how to reorganize the Faction if we use Sea Elves:
Tier 1: "Frogs" - tamed beasts
Tier 2: "Sea Elf Archers"
Tier 3: "Shark Guard"
Tier 4: "Water Spirits"
Tier 5: "Priestesses"
Tier 6: "Nagas"
Tier 7: "Giant Water Elementals"
Added 9 minutes later
or maybe like this:
Tier 1: "Frogs" - tamed beasts
Tier 2: "Sea Elf Archers"
Tier 3-4: "Shark Guard"
Tier 4-3: "Lake Nagas - warriors with shields"
Tier 5: "Priestesses"
Tier 6: "Water spirits or some kind of flying sea creature"
Tier 7: "Giant Water Elementals"
Units that can't swim should be numerous; these are the lizards and elves – the base of the Faction. Then, sea monsters at higher levels – these are sharks and witches, or maybe I'll calm down and leave everything as it is, who knows