Don't forget that if you can fit fewer Business Class Seats in the cabin, then there are fewer business class seats to carry along with less cutlery and china and booze, etc. I'm not saying this makes it the same as would be economy seating configurations, but it is a figure that needs to be subtracted.
In the same vein, don't forget that the UK Airport Departure tax is charged to flights departing UK airports and that the higher rate applies to any class higher than the lowest class on board that aircraft, so premium economy classes also pay the higher rate, yet all those business class-only flights are only liable to the lower rate.
Back to the transport industry as a whole; it's worth remembering that aviation is self funded including the infrastructure, whereas road transport relies on government investment (including the regular occurrence of car manufactures being paid subsidies). Railway transport used to be self funded, with infrastructure originally paid for by the private companies involved, but then governments took control (during the war), gave it back after a lack of investment (understandably) but then imposed tax charges for the land the railway companies owned!