Quote Originally Posted by Penta View Post
...Shouldn't we be designing the vehicles around the unit, not the unit around the vehicle?
In principal, yes. But since you are limited in vehicle width by public roads, you can only do two rows of seats vis-á-vis, and since you don't want to build the vehicle too long you end up with 2x4 + 1 troops and 2/3 drivers/gunners for an APC. And that is already quite a lot, since there are enough APCs out there that can't accomodate that number.
Same goes for helicopters (thinking about the UH-60 here, as the prototypical air assault helicopter). Two rows with 4 seats each, the squad leader between or besides the gunner(s), plus two pilots.
Only a irregular force can assume it never has to fit into any of these. For such units 18 on a open truck is not a problem, there you can go for large squads.