Why is the tmp the last MP to unlock in MW2... ?

it sucks. When I use it online, i have to reload every 2 seconds, it dosent hold very much ammo, and I have to put nearly the whole clip of it into someone to kill them. But yet, it's the last machine pistol you unlock... whats up with that? same with the RPG-7 in the launchers. What's so good about the RPG? it takes 2 hits to kill a helicopter or harrier with it, and its very in-acurate and long range for killing people with. And yet it takes longer to unlock then the javelin, stinger, and thumper. Can anybody answer these questions?