In that case, why build strategic bombers or the WWII bomber? Could collateral damage percentages be changed unit by unit?
Could the strategic bombers randomly destroy a building instead of doing damage, and with laser, target buildings?
Here's the thing... one must remember light bombers and fighters only target ONE UNIT at a time... they can't damage 5 or 6 or 7 units at a time like heavy bombers can.
Think about catapults... why does anybody use catapults? They can't kill anything... knights kill things... why don't people just use knights instead of catapults all the time... knights KILL! People use catapults for the collateral damage... something light bombers and jet fighters don't do.
Also, remember this... if I understand correctly, if I were to make a change to say light bombers and jet fighters could kill, that doesn't necessarily mean a single strike kills a single unit... I think you may still require multiple strikes by a light bomber or jet fighter to actually score a single kill (I think you still have a max amount of damage that can be inflicted in a single strike). Big bombers are still going to cause a lot more damage per strike... they'll just get to a point where they can't "finish"... but they'd still cause major damage to multiple units.
Remember... I'm only just scratching the surface here... thinking of options... would we really want heavy bombers that could kill every single unit defending a city before a single boot hits the ground? I know that in theory, you could do this with light bombers, but it would take a lot more work from them then it would heavy bombers if both had the ability to kill.
I guess the question you have to ask yourself... how badly do we want bombers that can kill? Remembering that naval and land kills are tied together (we can't choose), do we want to leave things as they are now, or start opening the "kill-all" box? Are we selective (only tactical light bombers can kill, while strategic heavy bombers just cause a lot of destruction), or do we open it up to all air units (every air unit can kill?).
Just thinking things through, not rushing to any conclusions.