I think I've been playing the Planetside games a bit too much, but when I learned ESO had a three faction war it was what brought me in after Tamriel Unlimited came out. Its been many years and each faction still feels the same on the field of battle despite each of the three races having different passives that lend to different game play styles. You could blame the Any Race Any Alliance pack but I've been thinking its not even that.
Using Planetside as an example all three factions have a common pool of vehicles and weapons they can pull from. This is like how in ESO we can buy and use all the different siege weapons we're familiar with into battle. While they have different adornments and colors they all function the same. In Planetside 1 and 2 though each faction also has special tanks, aircraft, and weapons only they can use. This adds to their faction identity and gives them great strengths as well as weaknesses. For example the Terran Republic specializes in Rapid fire machine guns and fast vehicles, The New Conglomerate uses railguns and super heavy vehicles that move slow, And the Vanu Sovereignty Uses alien weapons that are highly accurate and mobile but fizzle away at long ranges.
What I'm proposing is something similar but we don't need to fully copy another game as that is just silly. Maybe add a single special siege weapon for each side that only they can use. Maybe give the Ebonheart Pact some kind of Anti Infantry dragon styled flamethrower, The Daggerfall Covenant some kind of Lion siege weapon that inflicts bleeding effects as if they got slashed by a lion, and the Aldmeri Dominion could have some kind of Aerial attack Siege weapon. Maybe make it very weak but allows the person on the siege weapon to guide it in.
These are just a couple of ideas I had but what do you all think?
PC NA - Ceyanna Ashton - Breton Vampire MagDK