I say let there be a commander-like system that allows you to customize your roster and you have access to all three commanders at once. The catch is, it would used the CoH 1 system of CPs where you spend them to get access to certain items. This would leave whether you want to spend on smaller items first or go for bigger abilities ASAP.
Of course one could also make it a tree system where you need X amount of level 1s or 2s before getting level 3s.
Yeah i get your point.
I also thought about "customizable" doctrines, but it will just create doctrines meta where someone just create the god combination.
The point of, like i called them, "specialization" is to add diversity
Maybe some abilities/units of the commanders would be shared between sub trees, but there would also be a radical cut, so you need to actually decide the shape of your strategy.
You can customize your doctrine by choosing a specific path.
For example (just to give an idea, not necessarily balanced stuff what i'm saying), armored company commander would have among several sub trees
1) m10/bulldozer and 240mm
2) pershing, and smoke barrage
Both subtrees will share assault engies and other abilities, like a distinct feature of the armored company commander.
Luftwaffe doctrine will have fallschirmjager, ftfatherland ability, ostwind etc among other stuff for all subtrees, but than you need to decide if you want to specialize into cas (with strafe, at strafe and recon) or ground defense (with flak 88 etc...).
You expect airborne company to "spam" rocket loiter, but you can avoid "close air support" specialization and get the "airborne assault" specialization where instead if getting recon plane, strafe, rocket loiter you get a droppable weapon password locked weapon cache for para, a flare ability, the ability to drop at guns, but ALL sub trees belong to airborne doctrine, and will share some features like paratrooper mentioned above.
5 ability/call ins/passive would be shared, 5 would be specific of a specialization.