As JoeyB said, you'll probably need to use some gamey tactics to win. They only have ~ 400 transports according to your intel. Bring this number down to zero and then you can starve the 'doomstacks' in India. The easiest place to blockade significant troops is by invading Persia/Pakistan/India and fortifying the 1 province wide mountain passes. Maybe take Oman/Yemen and then Paratroop in to a province with a port but no beachhead. Alternatively if there are few beach defenders land on multiple beachheads but plan to consolidate to one or two provinces. If they pull the doomstacks back to engage your landing, retreat out your troops after hopefully killing a few hundred convoys and try again after the AI moves troops back to the front.