Hi folks.
I appear to have posted a solution to a problem I did not fully explain.(Its my age you know...

)
The original 3rd ed F.O,C was devised by
GW sales department to help new customers purchase minatures in 'easily recognizable batches' based on function.
I think there was some promotion where if you bought a
HQ unit and 4 troop units , you got a discount on a Heavy support ,or Fast Attack or Elite unit.(My memory is not 100% but I am sure my local
GW,( Nottingham,) had this promotion in the late 1990s.)
Every other war game I have played that has a wide variety of unit types, classes units by how rare they are in a particular force/faction/army.
This allows more thematic builds to be arrived at simply, and as each thematic list is independent, you can alter each list individually to arrive at the level of balance you need.
I think most people recognize
40k has awful levels of balance at every level.Even if there was a miracle and PV were assigned reasonably accurately at the unit level.
The complete lack of meaningful play testing means any sort of synergistic effects in the game are not accounted for.
So the external balance would still need work. (Spamming units to gain massive synergistic advantages, and people buying multiples of less effective units because of background reasons,ending up with a 'complete dud' of an army.)
Until the
GW devs completely gave up on the idea of game balance in 6th/7th edition.
GW used minimum amount of Troops options to force players to have to take 'less optimal ' units.The' Troop tax' as players with 'poor' troop unit choices might call it.
40k has a force organisation method that was designed as a sales gimmick to appeal to new players.But the only driver that would have improved sales, (discounts for army collectors,)was abandoned soon after launch.
So we were stuck with a restrictive force organisation method that would not let players build some ' narrative lists', and actively penalized some lists over others, right at the start.(Depending how good their 'Troops' choices are.)
But rather than fix the problem at source, with a completely new F.O.C. based on thematic lists and unit rarity within these new structures.
GW do what
GW always do!And add more complication to the system with ,Detachments,( Combined Arms, Allied and Formations,) and 'unbound, lunacy'.
(I did see a man in a
GW shop try to use Venn diagram to try to explain force organisation in
40k to a new customer!

)
Failure is not a lack of success, but a lack of effort.
IMO,
GW have failed at game balance in
40k completely.
The Idea I posted above was used in Epic
SM.Where players would start an army with a 'Company Card', which had a
HQ unit and several common units that gave the company its name.Then they could select several Support unit cards, and a Special unit card.
So for
40k we could take that basic idea to create the 'thematic core' of an army .
EG an
IG Armoured Company could have.
HQ unit
A Leman Russ Tank.(With Colonel or Commissar.)
Common Units
1 to 2 Leman Russ Tank Squadron.(2 to 3 Tanks each)
1 to 2 'Iron Fist' Mobile Infantry Platoons.(1 to 3 Squads per platoon.)
1 to 2 'Sentinel' scout Squadrons.(1 to 3 vehicles per Squadron.)
Support units
Infantry
0-2 Iron Fist Mobile infantry.
0-1 Ogryn Shock Assault (In Chimera Transport.)
Armour
0-2 Tank platoons.(1 to 3 tanks of the same variant. Leman Russ variants, or Hell Hound. )
Artillery.
0-2 Artillery Batteries.(Each Battery can have 1 to 3 vehicles , Griffon, Basilisk, Manticore )
Recon Units.
0-2 Salamander Recon A/C.
0-2 Sentinel scout squads.
Specialist unit.
Air support.
0-1 Vulture or Vendetta.
Doctrines.
'2 by 2.'
For every 'Tank' platoon taken ,(Front
AV 12 or higher.) There must be an infantry or recon platoon taken to support them.
Armoured vehicles are sitting ducks to long range artillery without good recon units to spot and neutralize them.And armour is easily destroyed in close confines of built up areas and heavy woodland by enemy infantry that is allowed to get too close.
This is just an example ,to show how themed lists do not have 'troop tax' .But allow a themed force to be built around a simple principal/concept..