I would say it's pretty stupid -- frankly: I think flying boats have their uses. That said, I can't say that land-based aircraft don't have their uses: They often out-performed their seaplane counterparts as they could carry weapons internally using straight-forward arrangements.
I'd definitely value a flying boat for the following jobs: Rescue, Sub-Hunting, Merchant-Raiding, and missions that require the ability to operate at a fast tempo (able to refuel and re-arm at sea); if I was planning on hammering targets close to land bases, and bombardment of land based targets -- I'd take the land-planes.
Depends on your point of view
In the late 1930s the goal of the USAAF was not to defend the country but to split off from the army and become an independent and equal armed force (if not superior) to the army or navy. . . . The whole rational behind the B-17(or other large bombers), as put out to congress (and public) was defending America's shores far out to sea (bombing invasion fleets) , not bombing foreign lands.
Of course, and that was basically nonsense: The entire goal was to attack targets that supported war-effort (airfields, harbors & docks, railway yards, and oil-refineries, power-generation, etc) and the civilian population and where they resided.
When an airwar is to be executed the USAF will run it, it's part and parcel of our core competencies. The entire airspace structure, air refueling tracks, targeting, deconfliction of air and ground assets (artillery), asset protection, ETC.
The goal of independent air arms usually was to control everything that flew, but often exemptions either existed or were made for various reasons
- Royal Air Force: They pretty much got everything, except (maybe) scouting used on battleships initially. It didn't work well as Coastal Command (despite the obvious importance to an island nation) didn't appear to be well funded, and the Fleet Air Arm was restricted by the Washington Naval Treaty, which limited the size and number of aircraft carriers (and this in turn reduced the demand for large numbers of carrier-based aircraft, and the R&D needed). While the USN and IJNAS were limited by this as well, both had the advantage of funding their own air-arms, which gives a natural desire to see it well funded and equipped (think of it this way, if you had to fund two places: One was your house, and the other was some guy you don't even get along with all that well -- you'll probably first take care of your stuff first; then take care of his stuff next), and the USN also managed to get the USMC to agree to procure (largely) naval aircraft, which basically drove up the supply and demand. In the late 1930's, they regained control of carrier based (and possibly other ship-based) aviation
- Royal Canadian Air Force: Apparently artillery spotting aircraft were procured for the Army's artillery spotting duties.
- Luftwaffe: It seemed they got everything except scout-planes used on Naval Warships. The history of Germany's re-armament was quite fascinating as it was largely a cloak and dagger affair until they kind of let it all hang out in 1935. They actually developed an aircraft carrier (Graf Zeppelin), and were at least in the process of navalizing several aircraft to this effect. Unfortunately Goring wanted to pretty much control everything that flew and the Kriegsmarine didn't seem to agree with that kind of thing.
There was also the USAF: Aimed initially to pretty much absorb all USN aircraft and sink all the carriers and relegate the rest of the USN into a glorified coast-guard and submarine-service, it was beaten back through some creative methods. The USAAF basically became the USAF excepting some transports and observation planes, which the Army got to keep until 1967. Helicopters were relatively new, and the USAF initially gave them weight limitations they could work with, and the US Army eventually managed to wiggle out of such restrictions and started arming their helicopters.
With one of the AF's roles being CAS: There were shitloads of problems involved that involved both services. In Korea, the decision-making authority to launch air-strikes was placed fairly high up in the Army's chain of command (under the belief that it was the best way to coordinate resources to the maximum effect), and might very well have produces sluggish response times. The USAF's coordination with the Army was quite poor at the time. After the Korean War, the development of smaller nuclear weapons and the New Look resulted in a decision to develop interceptors, bombers, and nuclear-strike capability, but CAS operations were poorly funded as part of national policy, and the fact that the bomber generals got a lock on the budget. It got so bad, that the US Army wanted to take over the CAS mission entirely (the sad part is, I'm not entirely sure that would have been a bad thing) and, while they lost, they would attempt this again by procuring the A4D-2N for this role, and the N-156F as some kind of scouting aircraft (which strikes me as a secret way of developing fighters), and were ultimately defeated as a result of this. Ultimately in 1967, it would appear that the USAF took control of most all fixed wing aircraft in exchange for the US Army being allowed to arm it's helos without restriction.
The US Army, USAF in particular, but also the USN, had issues with the use of land-based and sea-based missiles. There seemed to be no dispute that land-based aircraft were the preserve of the USAF, except when it came to the CAS issue, otherwise the problems were enormous. The USAF wanted to control ballistic and cruise missiles, seeing them as extensions of bombers, and SAM's, seeing them as extensions of interceptors. The Army saw SAM's as part of their role of AAA, with some cruise and ballistic missiles being an extension of offensive artillery. By in large, the US Army largely won this round: By 1956, the Secretary of Defense decided that missiles with ranges over 200 nm were the USAF's territory, and those under were Army territory -- after Sputnik -- the requirement was lifted, and they pretty much got control of all ABM development (ironically the Sprint missile looked almost like a dead-ringer to Project Wizard, which was the USAF's ABM project of choice): I'd say it worked out pretty well as Project Sentinel/Safeguard (I forgot which one was last) came in on time, and to cost (not something one can say about most military projects of any military service branch), and they got a national defense mission that didn't just include holding the population down in the event of the expected nuclear war that would see lots of awesome fireballs and spectacular bon-fires. That said the USAF managed some wins, including the "F-99" BOMARC, by adopting a policy of designating missiles as fighters (SAM and AAM) and bombers (ASM and SSM), under the creative idea that if they classify them as unmanned fighters, they get control over them (names have power).
Yes, I assume that you'll probably arrive at the inevitable conclusion that brevity is not my strong suit (and if you did -- you'd be right)