The strong probability of a 43 invasion is a deliberate game design and makes for a better balanced match otherwise the Axis would have it far too easy in the east. Historically its also accurate in that the Americans had planned for a 43 invasion before Churchill and circumstances had led them to focus on the Mediterranean and knocking out Italy. Indeed there was a plan for a smaller 42 invasion to be triggered if the Germans totally collapsed in the east. The one difference to the history is, as noted, the game 43 invasion hits with the strength of the real 44 one.
Axis strategy should be to either mitigate the possibility or delay it and/or reduce its strength by Sealion, a vigorous use of the Uboats backed up be surface forays, and offensive success in Egypt and a move into Irag therby diverting Allied energies. Helped of course if Spain joins the Axis.
A 43 invasion, even a powerful one but hopefully reduced through the above means, can be defeated if a powerful enough garrison with armour and fighter support and helped by coastal fortifications is gathered in the west by that date.
We know all that & are experienced players, both of us have all the other SC games so know how to play but so far can't win this one, the allies always seem to have level 4 or 5 fighter, Russians always seem to have a never ending supply of troops.
43 invasion is not historically accurate, it was abandoned due to the fact it would be imposable to do, that's why they decided to invade in 44. When your successful in Africa in 42-43 you will get invaded in France in early 43 instead of Africa which makes no sense. The AI doesn't put up a good enough fight in Egypt or Irag once the Germans defeat them.
The game would be more balanced & historically accurate if the allies invaded Africa then Italy & then Europe. There needs to be more of an effort made by the AI in Africa before any invasion of Europe. Africa should be in Allied hand before any landings in Europe is even considered.