In Empire Earth unit upgrades (with some exceptions) are tied to the unit individually and as a result the unit all you have do is click on the unit to see all the upgrades you have and purchase the upgrade you need.
(This image has been modified and is not 100% accurate to EE)
i: The miniature thumbnail shows that the unit has an available upgrade.
ii: Shows that the upgrade is being researched and its progress. Important for timing fights.
iii. Shows that the upgrade is queued but not currently being researched. For example, if you queue the Paladin upgrade behind 12 Cavalier upgrades, it would show the number 12. Clicking the Paladin upgrade again will move it to the front of the queue. Triple-clicking it will cancel the currently researching Cavalier upgrade so the Paladin upgrade can be researched instantly.
iv: The icon is darkened to show that the upgrade is unavailable. The icon also indicates that the player must age up and build a university to research this upgrade. Without those icons, new players might not know that they need a university to research Ballistics.
In AOEII, in order to upgrade a unit you have to click the unit to see its stats see what is missing, but it is unreliable because some upgrades do not visibly change a unit’s stats (e.g., most Monastery upgrades, Ballistics, Chieftains, Royal Heirs, and Lamellar Armor). You then have to press the hotkey for the building (or click the building itself if you haven’t memorized its hotkey), and then click the upgrade. This forces you to deselect the unit(s) wasting time and APM. Additionally Nearly all units are upgraded in multiple places. For example, Villager upgrades are purchased in up to six different buildings, with unique techs. As a result, you would have to select up to 6 different buildings to purchase or check upgrades for a single unit.
In my proposed system, you would simply select a unit, then press U. This would replace the regular unit UI with all the upgrades that can be purchased for that unit. For example, you would select a Villager, press U, and then be able to see and purchase all available upgrades for that one unit. This also could work with buildings you could purchase murder holes as long as you have a university.
This is not replacing the old upgrade system you can still purchase blacksmith upgrades at the blacksmith. But i believe that my system is way more friendly to new players, and viable for old players while still allowing them to stick to old system if they don’t like the change. But consider how often Nicov forgets Horsecollar well into the Imperial Age i think this is a better system for pro players as well if they are willing to adapt.