Nope they are not, they are lazy and soulless. AOE 4 is not a browser or Gmail which are task completion Software which has universal purpose in human society . It’s a videogame for entertainment purpose, that is themed around historical Middle Ages. AOE 4 is also used by a group of niche RTS players and it’s not gonna have core regular audience that will span across the planet.
Modern doesn’t mean it is good. Icons are there to communicate as OP as showcased here, icons here in AOE4 doesn’t work unless they have a tool tip. Icons should convey the theme and approximate topic by looking at them. These icons don’t do that, thus they are useless.
AOE 4 is a game that will be purchased by users to have entertainment experience and these type of icons are doing opposite. Gmail and Browser are free and their experiences wither away after few mins when the task is done.
Those applications use standard icons, like close, send, drop-down, Check mark which are not thematic and they convey immediate actions. In AOE 4 icons are thematic as action on what it does comes after the unit is produced and when the user can actually see the unit/tech/building and them in action in real time (Real time Strategy).
Clicking on the icon to have an effect is a well known fact to user, because the tiles are like buttons, thus icons are not doing the job, but the styling of the tile.
Thus setting the expectation and a theme for the upcoming user action will be taking, is very important. Detailed icons also add more to the human memory than generic same looking icons.
Flat type style is meant for generic actions and generic actions are less in this world, as contextual action are more in this world, but rate of usage of generic actions are always higher. That is why such actions use simple icons like an X mark, down arrow, Plus, Minus etc.
Stop being a blind fanboi and start demanding from your entertainment products. It’s a game where you pay and play for hours, by taking time from your life, so start demanding experiences. Companies and devs are not your friends.
Detailed icons need creativity, imagination and here even though the designer has done abstraction and simplification they have failed at it, as AOE is not an open ended narrative like Pablo Picasso’s painting or a Cave Painting from Altamira.
AOE icons are meant for communication. In a APM heavy game, nobody has time to contemplate on the meaning of an abstracted icon.
Things one doesn’t like and that can be done in a better manner needs to be called out and brought to attention, even if it does not make any change.