You know how it goes in 90% of matches:
English: Council Hall → King’s Palace → Berkshire
French: School of Cavalry → Guild Hall → Red Palace
HRE: Aachen Chapel → Regnitz → Palace of Swabia
China: Some initial variation but then always → Clocktower → Spirit Way
Rus: Golden Gate → Abbey of the Trinity → High Armory
Mongols: Deer Stones → Steppe Redoubt → ? (they always win before imp, lol)
Delhi: Besides Dome of the Faith, I do see some variation here.
Abbasid: Mostly economic wing → Culture → Military
Here’s an idea I’ve been toying with:
Instead of nerfing OP landmarks (e.g. Regnitz) or buffing crappy ones (e.g. Abbey of Kings), force ALL landmarks to have some kind of drawback. If you make the wrong landmark choice, you’re toast. Right now, at worst landmarks just sit there doing nothing (e.g. an empty Regnitz).
So let’s say you choose the Council Hall to mass-produce longbows like 99% of English players, that means you’re focusing on ranged units, so building that landmark causes you to lose the Elite Knight tech, or the last melee armor/attack blacksmith upgrades.
Another example: You go heavy on a strong economy as French or Rus (Chamber of Commerce, Golden Gate, Guild Hall, etc.). For having OP economy you forgo access to strong late units, instead having to mass-produce weaker, cheaper units.
Delhi’s Dome of the Faith produces Scholars 50% cheaper, but slightly increases villager production time.
You have superpowered siege as a Chinese with the Clocktower, but you don’t have springalds (your extra-ranged bombards have to compensate).
Etc… There’s a ton of creativity to be applied here, but I hope you see the idea: choosing a specific landmark should force you to make better strategic choices that can really come back to bite you if you didn’t scout properly or your enemy chooses a way to counteract.
The fact that all civs have access to basically the full tech tree no matter what is a terribly dumb choice (and a stark contrast to AoE2), plus in almost all matches you are guaranteed to know what landmarks your enemy is going to build. This too could be a good way balance Mongols and other OP civs without applying a civ-wide nerf. It would also completely change the team games dynamic since your teammate can compensate for a unit you’re missing while you can help support their economy.
As a closing comment, some landmarks still need some sort of buff of course.