The Galactica for the first time in the show is actually near full crew strength after absorbing the Pegasus crew.
Yeah that's why it bothered me when they did an episode where the deck crew is very overworked, I would think that if anything they had too many people after getting the Pegasus crew.
The problem is neither Galactica nor Pegasus were anywhere near close to full strength during the battle of New Caprica. Both operating with a third...a quarter of their crew? I think it's established in dialogue, or in a deleted scene (David cgc
would know better than I).
So, even when the crews were combined, they weren't at full strength. Yes, no doubt they picked up people from New Caprica, but something like 10,000 were lost there (IIRC), no doubt a number of them former military people. Add to that the Circle's rampant executions (i.e. Jammer) in "Collaborators" and you've got a recipe for too little manpower.