I think that the Major IC is only worthwhile if you are doing an “all-in” Barbossa strategy (one that does not involve buying a fleet with the Germans on G1).
In our last game, the German player did a standard CV, 2 Transports buy with the Germans on G1 to force the UK to pull everything back in defense in London. The second turn he bought a major IC in Romania and attacked Russia on G3. While the Major IC was helpful, he used too many resources early game between the Fleet buy and the Major IC and was not able to topple Moscow before the US was fully in the war.
I think that the Alpha 2 setup makes the Major IC buy helpful, but not necessary. If you are aggressive with the Germans and capture the Minor ICs in Russia, you can pump out all the tanks that you need in the later turns with your newly captured IC’s. Again, if you are going with a true Barbossa, I think that buying the Major IC is only worthwhile if you forgo buying any fleet on German G1.