... Balance was screwed and suddenly hard to tune because the first factions were meant to fight each other and none of the new factions. CoH3 balances each faction against two others from the start. This should hopefully reduce overfitting and allow easier introduction of new units and factions.
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Balance was screwed because Relic did a basic mistake. Instead of tuning the new faction to the old one they started tuning the old faction to new and that creates issues for a number of reasons.
Firstly neither USF nor OKW where balanced when released and that trying to fix thing by making changes to Ostheer/Soviet was a fools errand.
In addition "fixing" Soviet to fight okw and OStheer to fight USF meant destroying the balance between the two which Relic had spend so much to achieve.
The end result was to completely redesign 3 factions and waster more time in trying balance things while not fixing simple things.
Trying to release 4 faction at launch does take a lot of resources and might be a contributing reason why other things that should be easy fixes where not done upon release.