Think of things this way: How many fully geared up paratroopers could a C47 carry? How many troops could an M3 carry? Jeep? LVT?
I think there should be more of an emphisis of capturing an enemy base via the C47 than with the M3/251. So, my suggestion would be to raise the capture minimum to 15 and allow the C47 to carry 15 paras, the M3/251 the capability to carry 12 troops, the jeep keeps it 3, and the LVT's get to carry 8 troops. Those who have been in the back of the "Deuce and a half" trucks know how cramped they are and they carried 12 fully geared up troops (M3 is the same). Someone correct me if I am wrong, but the LVT's carried no more than 8 marines to shore at a time, right? I can hear the calls for maxing the C47 out with troops if we're going to play the "realism" numbers and that would be fine. I'd have no arguement with that, really. I would seriously make you use your MG's and having 20+ troops running to the MR would cause a ruckus, no doubt. Matter of fact...I say go for it. Likewise, I say allow the C47 to carry TWO loads of fields supplies and perhaps 15 vehicle supps.
(can you hear all the gasping and inhales for in the impending screams???)
Variety and realism are my 2 big reasons. Currently, there are far too may "1 man shows" in base capturing and the M3 allows for that in a very easy manner. There is no variety as they all carry the same number of troops 'cept for the jeep. If there was variety, it was cause the quick base grabs to slow tremendously, it would take more coodination and team work to get multiple M3's/251's and LVT's to the MR.
Right now... things are very much a rubber stamp. Change it up.