It definitely needs to adapt to the role model of the ship.  

It also has an AoM influence. The game was still in its conceptual stage in 2002 when Age of Mythology was released.

Precisely because of the golf carts and other vehicles being used in the current war. That's why I said it.

But the game's symmetry also depends on how players can play the civilisations. Directly modifying the civilisations to push them towards more distinct playstyles than they currently have would, in my opinion, be the first step. Today, by sticking to roughly the same playstyle and the same build orders or unit orders, all civilisations remain generally playable. If we play the Carthaginians with a more Gallic playstyle, the civilisation remains fairly competitive. The only real differences between the game's civilisations at the moment are different but rather abstract bonuses (especially for new players), different textures, and a few unique buildings and units that don't fundamentally change the playstyles... In my opinion, we should (still) preserve 0 A.D.'s origins (AoE2) and draw inspiration from it. In AoE2 (or even AoE4), civilisations have things in common but still retain different playstyles! I haven't tried DE, so I can't say whether this mod adds differences between civilisations and meets my "criteria". What could make a difference, and what I also feel is missing, is the diversity and depth of Petra's playstyles, and I completely agree with you on that! But yes, changing playstyles depending on the civilisation would make balancing more complex, and I don't think the developers would put in the time needed to do that at the moment. Is there a mod that has experimented with changing AI playstyles? Anyway, we're starting to drift away from the original topic of the discussion 

I also find the game too symmetrical. What I believe needs to be changed and what I have experimented with changing is the behavior of the bots: small civilizations or vassal states should not act like great powers, and nomadic civilizations should not behave the same way as sedentary ones. The issue, however, is that such changes would make balancing the game difficult, and many players likely wouldn't appreciate it.