...except that the Germans would still have come unstuck in the 8 (or is it 9?) time zones east of Moscow, Russian Far East Army or not! And that's ignoring the worsening (for them) situation in North Africa. And the Japs could hardly ignore the USA because of the Philippines.
The Japanese, now being fully paid up members of the Axis would now be at war with the UK. Using Germany’s right of conquest over France and Holland they would occupy Indo China and Sumatra. These would be used as a base to overrun Singapore and the Solomon Islands which would ring fence Australia and New Zealand making their troops unavailable to the UK.
They did most of this and tried the rest. Losing at Coral Sea certainly hindered their plans in the Solomons, but had the Americans not offered battle (because they weren't in the war) it is far from certain that the Japs could have besieged Australia and NZ effectively.
What is lucky is that Hitler was so deluded as to declare war on the USA - without that, Roosevelt might have concentrated his attention on the Pacific and we would all be speaking Russian!
Whether Pearl Harbour was the key turning point or not, I guess Churchill was more qualified than most to make that judgement
His views at the time make perfect sense but he lacked the benefit of hindsight! Of course he was massively relieved to have the Americans dragged into the war, but he couldn't possibly have guessed how badly the German gamble in Russia was already backfiring.
Barbarossa was a tactical blunder
Or Strategic? Or Grand Strategic?