I think making units for the Commonwealth is going to be complicated but I like the intellectual exercice.
If I were to check the Commonwealth equipment, I think we see that overall (until Sherman) their vehicles are usually on the heavier side : Churchill or Valentine of course, but even the Cruiser II was slow for a "cavalry" tank.
On the other hand, as their tanks are also pretty heavy, and since their infantry is reputed for their grit, I think the doctrine is basically :
- Slow land units (-20% speed), more HP (+15%). So kind of the opposite of the Japanese.
On the other hand, the navy has normal speed but is all around better than the competition for Cruisers and Battleships (less so for submarines and carriers).
This means that :
- On a large map, the English player is encouraged to use his navy / convoy a lot to move around, as historically
- On a small map, where usually navy are less important, their speed is also less of an issue for obvious reason so it balances out.
Since we are there, if I had to do a doctrine for French, it would be OF COURSE defensive minded, no only for the Maginot line but also for their "bataille conduite" doctrine and their tanks which were very much on the heavy side.
Therefore, the French would have :
- 20% more defense value
- +50% defensive value of fortfication
- Excellent artillery but (critical for balancing) with shorter range so you cannot turtle easily behind artillery
In addition, the French are slow to adapt to new techniques, so they would have +20% cost in research cost & time and upgrade cost&time.
I would also remove the move speed malus of Americans (US materials and troops were not specifically slow, if anything the TD were the fastest) and replace by something like "risk adverse", combat cycles take 20% longer (eg 36minutes, slowing down their offensive and making them at a disadvantage when defending)