Hmmm.
I'd need to check the numbers, but I think that in that case choosing between Light Vehicle Light Bombardment and Infantry Light Bombardment is a question of if you want your LB units to have some armour against counter battery fire or if you will accept the greater losses for something like 30% more guns on target. Until you get armoured and power armoured infantry, in which case you want them. They're IIRC the same size as Infantry but as well armoured as Light Vehicles, so at that point? Unless they're ruinously more expensive it's worth the trade off.
Heavy Bombardment sees something similar between Heavy Vehicles and Static. Static units are notably smaller per component and can massively stack their Fortification, but Heavy Vehicles just have better armour. I expect this will come down to whether or not the local terrain supports fortification bonuses or not.