el-jasho do you mean that the other way round? Because otherwise...
Any possible combination of Heavy, Light, Operative and Soldier will be brutally effective in the right hands.
Light Op - well, obvious.
Heavy Soldier - also obvious
Heavy Op - defend objectives, Firewall CPs to slow enemy capture attempts, Hack comms when the enemy's downed, providing radar to all teammates, Sticky Bomb + enemy Operative = defensive utility. And spotting mines, marking them for teammates, easy way to help the team avoid a well-planned ambush.
Light Soldier = fast-moving with multiple grenade types and an additional health upgrade, so extra-durable, able to provide ammo to anyone on the front lines at short notice, and with proper use of grenades, he can hit hard, then scavenge to replenish his supplies (no need to fall back and wait, or call a medic over when you aren't hurt.
Light Soldiers will be an awesome class for sneaky hit-and-run tactics, and heavy Ops will be very useful in a defensive line. We may not SEE them often, but when used well, they'll still be great combinations.
Which is why I'm saying the Heavy SMG/Pistol guys are going to be the most rare. Not class-specific.