If we give the light cannon the base damage of 2400 you suggested and we would give the heavy cannon a base damage of for example 50 percent more this would give the heavy cannon a base damage of 3600. For comparison: At the moment with my mod in beta 05, the heavy cannon has a damage per minute of 2925 and its good playable. Your light cannon would have a damage per minute of approximately 6000-6500, and the heavy cannon of 9750 in beta 05. Three times the damage it has with my mod. If you think the assault gun is overpowered at the moment the assault gun would be a child toy in comparison to the heavy cannon you suggest.
err say what now no i did say give the light cannon a base damage of 2400 that would be completely insane, what i actually said was
the heavy machine-gun has a damage value of 30 after 3 upgrades, and the default value of the light cannon with out any upgrades is 40 after 1 upgrade with the changes you made that increases by 12 taking the damage value 52
and with a damage value of 52 and a rate of fire of 60 that would give the light cannon a similar damage per minute value to that of the heavy machine-gun
light cannon
52 x 60 = 3120 damage per min
heavy machine-gun
30 x 107 = 3210 damage per min
which seems like i might be a reasonable place to start when balancing the light cannon.
however if you take in to account the other 2 damage upgrade that would increase the light cannons damage to 76 x 60 = 4560 damage per minute which is probably a bit much.
however at the time i didn't realise i was still loading the mod and what i meant to do was
light cannon
damage without any upgrades 30
3 upgrades at 9 points each is 27
my rate of fire of 60
would give the light cannon a damage per min of 3420 once you apply all 3 damage upgrades
medium cannon
damage without any upgrades 60
3 upgrades at 9 points each is 27
my rate of fire of 30
would give the medium cannon a damage per min of 2610 once you apply all 3 damage upgrades
heavy cannon
damage without any upgrades 106
3 upgrades at 9 points each is 27
my rate of fire of 15
would give the heavy cannon a damage per min of 1995
however upon doing that i realised there is an issue with these values in that they are completely backwards which means that we would need to change the base damage values and the values of the upgrades so if we do
light cannon
damage without any upgrades 15
3 upgrades at 6 points each is 18
my rate of fire of 60
would give the light cannon a damage per min of 1980 once you apply all 3 damage upgrades
medium cannon
damage without any upgrades 70
3 upgrades at 9 points each is 18
my rate of fire of 30
would give the medium cannon a damage per min of 2640 once you apply all 3 damage upgrades
heavy cannon
damage without any upgrades 180
3 upgrades at 9 points each is 18
my rate of fire of 15
would give the heavy cannon a damage per min of 2970 once you apply all 3 damage upgrades.
if you factor in 3 more upgrade from beta campaign again at 9 point each then that would increase the
light cannon to 3060 damage per min
medium cannon to 3180 damage per min
Heavy cannon to 3240 damage per min
which is not bad, although with these values the heavy cannon is stronger than the lancer so I fully expect that these would need scaling back a bit especially if you want the damage ceiling to be no more that 2000 2500 for alpha campaign as opposed to a ceiling of 3000 for alpha campaign.
At the end of beta 05 with 5 damage upgrades and one or two ROF upgrades (ROF is 13 shots per minute), the heavy cannon has a damage per minute of 2925. At the same time, the lancer has after 6 damage upgrades a damage of 300 with a fire rate of 12 shots per minute giving him a base damage per minute of 3600. And I think this is too much why I wrote before we should decrease the base damage of the lancer to 100.
I'm not so sure that's a good plan because that may well make lancers to weak on alpha but what you could do on beta perhaps is decrease the amount that each damage upgrade gives which would have the same effect of bringing down the lancers damage.
with your suggested values giving the heavy cannon after 3 damage upgrades without any ROF upgrade a damage per minute of 3000 would give the heavy cannon a damage per minute of more than 4000 at the end of beta 05. 2925 per minute is good to fight the collective tiger bodies. Every body of the NP will be shredded into pieces in seconds with these values.
I forgot that you get rate of fire upgrades on beta although this isn't to difficult to deal with once we know how many ROF upgrades there are and how much they buff the rate of fire its simply a case of subtracting that from what i have already presented here which would eliminate that problem in short order.