Because all aircraft in controlled airspace must have a flightplan we can start with the assumption that the system is able to allocate airspace resources as necessary.
This illustrates where we begin to differ. That may be true where you are, but it's absolutely not true in the U.S. I need not, and in fact, rarely do file a flight plan for VFR flights in the local area, whether it be controlled airspace or not. I must contact ATC in certain instances, but there is no requirement I file a VFR flight plan any time except for operations around D.C. and certain other Security zones. My only "plan" when departing in my Skyhawk often involves only heading a certain direction initially, and then I go where whim takes me. That's still possible in much of the U.S. (Thank God!)
I can assure you that I am far, far from being a "maverick" in this regard. VFR Flight Plans in the U.S. are pretty much strictly for SAR purposes only, and almost never are forwarded to ATC. They reside at the Flight Service Stations. I dare say most pilots I know do not file VFR flight plans for local flights. Only for cross-country flights, especially in thinly populated areas. Even then, it's usually not a requirement.