Kannons can lob an unending stream of napalm nades into rooms, this firing mode should generate weapon heat per grenade tossed in order to limit it as currently its only limited by time to reload the next shell, which is an way too short mechanism to limit this weapon being spammed enmasse.
In fact, its the only of the area-denial weapons that has an firing mode that does not generate any heat per use.
Obviously this should be changed as its causing an imbalance between factions.

que all the ork salt and rage

It reloads every time in between nades that's why it doesn't have heat.

The Kannony Deffgun doesn't have heat because you have to reload it between shots.

Plasma Cannon can lob 3 shots in short succession and overheat (fire one, hold R for a second to vent a little bit of heat then fire off two more)

The Eldar Tempest is about putting multiple explosives down in the area/TKing your teammates.

We have orks in this game?

You clearly have never even used it.

It also occasionally bugs and drops it right at your feet. Napalm or regular. I've found bashing another Ork with it after to respawn but before you fire your next shot fixes that right up.