Y
That is the reason why I believe that Apple's cooling solution is pretty damn good. They chose a more complex design in order to make the laptop more versatile, even if this design is inherently less efficient than direct air suction through the bottom grills, and they still achieve a reasonable result. Funnily enough, one reason why it works is probably because it is so thin Its like a vacuum inside. It's quite smart IMO.
Bottomline: if Apple adopted a design like every other laptop and put inlet vents on the bottom, directly in front of the vents, then yes, the cooling performance of the MBP would most certainly improve. Would it make it a better laptop though? I doubt it. Many users choose Apple exactly because of those little things like absence of bottom grills. It makes the laptop just overall more useable.
This is probably an over simplification of the design choices Apple made
Whilst your assumptions on cooling are likely to be correct it negates the other issues that are equally likely simplified by not having vents on the bottom not least of all structural integrity of the chassis being so thin. It's also possible that placement of components on the logic board were simplified. It may also be a limitation and/or cost prohibitive aspect of the uni body design and materials
To imply all other aspects of design/construction are equal and Apple picked a more complex solution in isolation is unlikely.
There's no bragging rights here just the end result of many design decisions taken