I have noticed following unit types are excluded from all strategies and not available on default map (excluding Other and Rare unit types):
- Air: Commander (?)
- Air: Defence
- Air: Secondary Attack
- Ground: Commander (?)
- Ground: Secondary Attack
- Ground: Special Attack
- Ground: Support
- Ground: Transport
- Naval: Commander (?)
- Naval: Defence
- Naval: Secondary Attack
- Naval: Special Attack
- Naval: Support
I've tried to find those units on custom maps and found out that -50 cost reducement applies to all Support units and that Ground transports get HP boost too. After applying the changes to the list, we can see there are 10 useless unit types.
What is the point of those unit types? In old forum posts I can see Commander units do add some bonuses, but the units stated as being Commander type such as Air Marshal are actually Rare units. I noticed that Naval: Commander acts like General in naval battles, but I have no idea how it actually works. An input from mod would be nice on this issue.
I honestly think other unit types deserve at least 1 upgrade for them, otherwise they are all same as Other type of units.