Experience system

That is hard to implement as you merge units into groups and unmerge them all the time it will be cwry hard to keep track of which unit got how many kills...

This would be difficult, if not impossible, to do because even though you might get an achievement, it could have taken you years to do it. you also might have gotten it but are still a bad player. the achievements just say that "you have killed 500 infantry units" ect. but even with this your K/D ratio might be very low, or all those kills were against AI or inactive players. so experience would be very hard to do and maintain.