Please forgive me if this topic has been beaten to death, but I had an idea which could be a solution for ground combat.
So ships are designed. On one side you have Beamers, massdrivers and missiles and on the defending end you have shields, armor and evasion. Then you have special systems which you can develope and add. The more the heavier the ship will be and the more it will cost.
A similar system could be good for ground combat units too. They could have also beamers, massdriver and missile modules to build in. So they are compatible with the existing ship building system. So example a ground combat unit could have 2 beam modules and 3 armor modules and 1 missile module. As special systems maybe one can integrate "exosuits" for combat on planets with biological hazards and "gravitational lifters". So if on GCU meets another in planetary combat - just by moving on it like ship combat or better invading the enemy planet hex- the combat mechanics are the same as in ship combat. Beamers are good for shields etc.
One can consider ground combat units with a lot of modules are as heavy and very big armies, while small ground combat units with a few modules can be considered as divisions or brigades.
A big advantage is that the combat ships and ground combat units can interact with each other without developing a new system.
If this idea is already anywhere on this forum I beg your pardon I didnt read everything due to time shortage.
bye
klaus1416