Pol said:
The argument that the increments are too small doesn't hold up. As far as I know there are 54 techs to be researched and that means there are massive gains to be made. Germany benefits considerably from having such excellent tech teams and can keep up reasonably well in other fields.
As Germany, you really only have two tech teams that are viable for land doctrines (albeit they are very good teams): Manstein and Guderian. These are also, not coincidently, the same teams you need for Infantry and Armor research (respectively). Given how long it takes to research each land doctrine, if you try to keep an historical pace with land doctrine research then you'll fall behind in the far more important (and useful) Infantry and Armor/Artillery trees.
As they currently exist, the land doctrines simply take far too long to research for the marginal benefit that they each provide. There are several ways to fix this. The easiest is to make them take less time. The (IMO) better way is to redo the tree so that each tech is more focused on particular aspects of land warfare (such as supply, fortification, et cetera). This would have several excellent benefits. It allows for more inspired naming of each tech. It allows for a better focus so that each nation can tailor itself to a particular style of warfare. And, not least, it allows for a larger bonus to be applied to fewer aspects, so that when you've researched the tech you feel you've accomplished something that you'll notice on the battlefield.
I assure you that the current 0.5-1% boosts in org, or morale, or whatever (and I know that you get such boosts to each of 10-20+ different aspects of land combat) are, with the exception of TC, inconsequential in the game. You won't notice their impact. It doesn't matter that after researching ten or twenty land doctrines (which takes an horrendous amount of valuable tech team time to do) you'll have some appreciable bonuses (and that affect all aspects of land combat). Had you spent that time instead on researching in the Infantry, Armor, Aircraft, Air Doctrine, and Industrial trees you'll be by far more effective in combat. I've tried it both ways (researching or ignoring the land doctrines) in 4 separate games (twice each way, just to be sure). The current land doctrine system needs tweaking. And IMO, it needs it badly.