The rest of the code seems not too great either, considering the humongous system requirements, compared to the historical versions of the game. If you ask me, they could have kept it 2D sprites and it would have been completely fine. But they had to go 3D ...
I'm with you on the system requirements bloat. Really sad honestly. That said, I don't think the engine is more 3D than it used to be, is it? I believe it's still isometric 2D with 3D physics. Could definitely (definitively?) be wrong though.
Here's some discussion on it: https://www.reddit.com/r/ageofempires/comments/16aowwc/are_t...
To me it looks kinda 3D, when you pane left right and look at buildings, but I could be wrong and that could be merely some effect, that also takes some on the fly calculation.