I tried this in a face-to-face game against Karl7, who of course is very good with the German pieces, and wound up losing Moscow on G6 on a German attack that had 91% odds – but Germany lost about 80% of its stack taking Moscow, so it was likely that the Middle East would have held, and almost certain that Cairo would have held. We ultimately scooped at least as much because the Western Allies didn’t have a sufficient compensatory attack as because the German drive was unstoppable. Like, the Allies were able to barely take Rome on UK6 using a one-two punch, but trading both Moscow and Calcutta for Rome is not a good trade.
I think my main mistake was that on R2 I placed slow movers up front in Vyborg with fast movers behind the lines in Leningrad, with the idea of maximizing my threat to Finland. This might have worked fine if the Allies were swarming toward Norway, but the British Atlantic fleet was wiped out, there were German subs in the Atlantic, and the British and Americans were both focused on beating up Italy in the Mediterranean. Without Anglo-American pressure on Norway, the Russians can’t afford to invest too much against Finland. Karl7 was able to temporarily retreat all Finnish forces into Norway, and just come right back to Finland after Leningrad was dead zoned by the advancing Baltic States stack. I held Finland for one turn, and then I wound up with 10 slow movers stuck in Vyborg, unable to either kill the reinforced Finnish stack or safely stack up in Leningrad.
What I should have done was put the fast movers in Vyborg and the slow movers in Leningrad – that way I could have moved the entire stack to Archangel or Belarus to join up with the rest of my forces to form one mega-stack capable of temporarily holding out against the main German forces. Instead I was defeated in detail. All of my armies except the 10 inf/art in Vyborg and a blocking force of 4 inf + 1 AAA ultimately made it home to Moscow for the G6 battle, which is a somewhat impressive recovery rate (if I do say so myself) given that I was playing far enough forward that Germany wasn’t able to build any units in either Leningrad or Kiev until G6. Still, 15 armies is still too many to lose when you’re building mechs; the point of mechs is to get damn near everybody home.
I’ll try the strategy again with the proper configuration of fast and slow movers in another game and let you all know how it goes. Keep the faith! The Allies will find an answer to the German mech/tank rush.