@AndrewAAGamer I think it was a mistake for him to build the inf in Leningrad last turn as that stranded those units. But now that they are there, they cannot reach Moscow, so we can’t count them against the fighters in the defense of Moscow. The tanks and mechs might make it back since you are committed to the southern route but that is unlikely. Although they likely do trade against some of your other land units.
We can probably do a pretty good estimate of the odds in Moscow on this basis. If you take the stack that can reach Moscow on G6: 32 inf, 22 mech, 11 art, 16 tanks, 5 fig, 9 tac, and 6 bombers and you take what he can conservatively stack there:75 inf, 3 mechs, 3 art and 2 fighters + 1 tac you get 100% odds. If you add 4 British fighters and two tacs from the Middle East and India and the two allied bombers, you get 92% odds. If you add 5 more inf, 2 tanks and 1 mech (that would be saved had he not gone for Karelia and blocked Leningrad it goes down to 50%. However, if you take Leningrad and you can build an extra bomber your odds go up by about 10%. So you would end up at around 60%
With the 6 fighters instead of the Soviet land units (5 UK and 1 Fr fig) and holding Leningrad (which likely denies you another bomber) it goes to 40%. So there is a difference on G6 of about 20%.
I doubt you would attack with anything less than 90%+ odds, however, and I think you would have trouble maximizing the spending to hit Moscow with this much anyway (I’m assuming a 4 tac build this turn and 4-5 bomber build next turn which would be hard to sustain given the pressure that will be coming in the atlantic.) So that your odds are not yet high enough is an argument to have held back on landing the fighters in Karelia and plan on being able to send fighters either through Norway or the Med for a G7 or G8 attack. But he also has to worry about a strat bombing and its better if he can keep some air to contest Japan’s moves in India and potentially the Middle East. And small differences in the number of defending or attacking units can make a huge difference in what those odds are. If he couldn’t build 4 inf because of a successful strat bombing and 1 of those UK air in the mid east can’t reach Moscow your odds on G6 are almost back to 90%
You are definitely right that he also needs those air in the Atlantic. It is best if they are in Gib or London, but from Karelia they can at least still reach 110 and if he goes to Moscow they can still land in Norway on UK5. And since you are likely not in a position now to spend solely for an attack on Moscow, he can pull some of that air back on the subsequent turn.
Saying all that I think it probably would have been better to focus only on Karelia, give up on Leningrad and try to retreat everyone that he safely can. But he plans on making trouble for you in Scandinavia which, if Moscow lasts long enough, can end up being worth it too.