Yes you can go up in rank with another kit.
i.e.
My medic is maxxed out. But dropping a med pack or ammo pack is a sure way to get tons of points, or engineer/c4 near an mcom(not too close) to get defense poitns when they go off in nearby explosions.
So I spawn as sniper, use motion balls often to highlight, get points that way, try a mortar strike here or there for harassment, but really, search out kits of Assault or Medic. If I happen upon an engineer so be it, I layout a few mines.
I then pick up an assault kit, drop ammo pack, then a medic kit and drop meds.
Then I sit in the corner and rake in, Med points, Ammo points and Mine hits/double kill/tank kill/ defense double points on top of that, its like a slot machine when the score dinger is going!!!!!
This has helped me upgrade Eng and Sniper.
The only time I use an MG (since I too hate them) is when I pick up a kit, and its good to be a sniper Medic because you dont have that silly beret on top
I also use the assault kit with Smoke often, my points are low but its for my clan to win. I smoke the heck out of the map and sniper spots so they cant see either. I have practised to launch smoke from the spawn onto the objective by using trees or mountains as reference aim spots. I too am surprised how FEW people use smoke, non team players!
I get annoyed at the M60 sprayers, but with the M60s and Gustav's you just have to account it to noobness. Other guns require more skill to use and make it more challenging.
The AN-94 with the +handle to accurize its recoil is a killer rifle when using headshots.
I still use my M-1 garand when able in all classes, its more rewarding for my 1-2 kills per game