I think the very first thing to do is identify ALL the branches of combat; aswell as the Doctrine's role; I'll explain it the best way and feel free to make adjustments.
First of all; we need a clear distintion between units; what belongs to what:
E.g. for branches; some can be merged.
2) Half-Tracks/Armored Cars/Light Tanks.
3) Medium Tanks/TD's.
4) Heavy Tanks/TD's.
6) Air Support.
Also, you need to take into consideration the Doctrine's role; one primary role, with elements of the ascending one;
1) Defensive. (Emplacements; Sector Denial; Fortified OP's construction...)
2) Supportive. (Indirect Fire; AA/AT measures...)
3) Offensive. (Elite Elements; Spearhead Push...)
With this; either you have a doc's role with DEF/SUP Elements; SUP/OFF Elements... BUT NO DEF/OFF.
So, by taking this 2 aspects you can make the decition regarding the question about "Specialized vs. Well-Rounded";
If the gameplay is meant to be based on TEAM-PLAY (NOT a 1v1 match), then, a Specialized aproach is better... but as you said in a post using the "Rock, Paper and Scissors" metaphor; What happen when there's a "Doctrine Hole" or a "+1 element" in a 4v4 match? It's hard to compensate. But take this 2 points;
Take a look at this;viewtopic.php?f=27&t=1776
I know, Panzerblitz said it's just a tool for newcomers; but here's my view:
You can take this elements; ROLES with their BRANCHES; distribute them among the 6 doc's of each side, getting an equal match for both sides:
You can have same ROLE but with different BRANCHES;
-DEF DOC and RE DOC:
->Same ROLE with Emplacements.
->Differ in Artillery Response.
I know it's over simplified but stick with me:
Take by example the WM doc's:
1st; Defensive (Bunkers, 88's EMP's, Cheaper Mines/Goliath, Stronger OP's, Dragon's teeth/Roadblocks...)
2nd; Supportive (Limited Artillery response, AA halftracks, Möbelwagen)
1) Infantry. (Volks as Backbone; G43's instead of MP-44, and so on...)
2) Half-Tracks/Armored Cars/Light Tanks. (Only Sd.Kfz. 251 variants to deal with multiple threats...)
3) Medium Tanks/TD's. (Jagdpanzer IV L/48 and Marder I)
5) Artillery/SPG's. (105 Howitzer/VT)
1st; Offensive (Elite Infantry, Good Medium Tanks, BK Assault)
2nd; Supportive (Frontline Artillery, AA Puma/Ostwind)
1) Infantry. (Stormtrooper as Backbone)
3) Medium Tanks/TD's. (Pz IV's variants)
4) Heavy Tanks/TD's. (Tiger)
5) Artillery/SPG's. (StuH)
1st; Offensive. (Elite Infantry, Heavy Tanks, Zeal)
2nd; Supportive. (Rocket Artillery, AA Puma)
1)Infantry. (Grenadiers as Backbone)
4) Heavy Tanks/TD's. (Panther G)
5) Artillery/SPG's. (Nebelwerfer)
Adding the PE docs and their respective Doc's, you get some combos like:
3 Players: 2 DEF/SUP and 1 SUP/OFF
>Def Doctrine; Good with Emplacement but Limited Artillery Response.
>SE Doctrine; You don't get the Emplacement abundance of DEF; but you have the Artillery Response and Sector Denial.
>BK Doctrine; You get those Medium Tanks and Elite Infantry the other docs lack.
I know this is over-simplified, but I think you get the idea behind;
Clear Orientation for the Doctrine.
In what Branch is stronger.
Harmony between WM/PE and US/CW.
Another thing to mention;
The difference between BK and Terror is in Mid to Late Game.
If we implement something like this;
I agree with Warhawks in the matter of making the units more durable instead of more of a spam thing. The topic is worth a reading;
And back to my point in the BK and Terror "time";
Instead of a "Mass Production" unlock; a Vet1 might help BK doc in Late game; sure, it can't go frontal attack versus Pershings and Jacksons but with the mobility of a Medium Tank, all goes down to flanking tactics and waiting for the oportunity to attack, supporting the Terror's Heavy Cats.
I repeat myself, I know this is a lot of work; Revising all doctrines to fit either way of "Specialized vs. Well-Rounded" design is going to take time.
But my points are:
Define the ROLE of the Doctrine; Don't make it a Jack-of-all-trades. If it's Defensive; No assault guns, no heavy tanks, and so on...
Maybe 2-3 BRANCHES to excels in (maybe 4); 2 for the 1st ROLE; and 1-2 for the SUPP ROLE.
Changing "Mass Production" for a "VET UP" unlock; that way the ROLE of the Doctrine is worth more; The BRANCH is more durable. Thus, able to survive for a longer time, gain Vet, and helping in Late Game. Encouraging TEAM PLAY.
This is just my thoughts on the matter.