far from performance thing, here’s whats going on based on how stuff like placement and map generation work
aoe3 has free place and no forced grid in place which allows for free building placement and for fog of war to unveil in a smooth manner with no sudden jumps
aoe4 meanwhile is using aoe2 like grid system, but grid itself is less dense in 4, small jumps occur when tiles are unveiled in 2, same with 4 but those jumps are bigger as the grid isn’t as dense for map gen. or building placement, the only exception being the walls which divide each tile into 16 or so smaller ones
as for that fog effect, thats smt devs aren’t particularly open to getting rid off, unless they do this:
i don’t see any fog on the image from anniversary update stream, so this imo suggests we’re looking into another case of developer not implementing certain settings outside of dev only versions of the game, along side zoom levels and angles on these 2 screenshots
back on topic, i highly doubt the bigger grid has anything to do with performance, instead it was done so i assume before any building or any other asset was made, right at the start of the development, not exactly smt you can easily correct now