Soldiers should be rewarded with bonus xp from doing action related with their profession:
Infantry: point flip or conquest
Engineer: spawning troops, building on contested point, ammo resupply
Assault: killing on contested point
Sniper: headshot
Flame troops: flamethrower kills
Lmg: suppression? Lmg kills?
Radioman: artillery kills
Antintank: tank and cars kills, antitank weapon kills
Mortarman: mortar kills
I never ever use tank or planes but they get so much kill i literally dont know how they can earn more