You might also have added that Montgomery seemed to ignore the Canadians, who did the heavy lifting, for instance at 'the trial' of Dieppe, or by clearing the Scheldt. And Canadians were also a heavy punch on D-Day. though equally, it was the Canadians who did not quite complete the block at Falaise (correct me, please, if you think I am wrong).
That is why the commonwealth should in my opinion be one faction, so as not to forget about our brothers who fought so gallantly as well.
We talked before about possibly having a commander for each nation and maybe also the free french/ poles etc. But this could be complicated to balance, and cause many issues such as similar units.
Personally I think they should make use of randomized infantry sections that function the same but could come out as anything from Englishmen to Scottish highlanders or even Canadian, Aussies or Indians etc. This would fit with the whole ideology of the British having to make do with what was available at the time.
Not sure how else they could represent all the nations that fought, without inevitably forgetting others. To be fair as well, think about it from the leadership point of view, Alexander at Monte Casino for example had a real mixed bag of units and nationalities to deal with, but that didn't stop him (as mentioned by BeltFedWombat)