This is BY DESING and its called the low spec mode , wich bring a lot of fps and less clutter but it looks bad.
And barely its on 60 fps lol . Hey just dont lie ok? You can play gta trilogy and at every 5 minutes you notice like 10 visuals bugs and im not even kiding , just search in yt.
In fact aoe4 doesnt get its optimization by the zoom level neither , this was confirmed in the closed beta using a tool in game that let you zoom out whatever you did want , the current zoom level is fine for 4k users , not as good for 1080p users though but its playable .
The optimization has nothing to do with the zoom level .