This is patently untrue Loon. Virtually every plane in the game can employ flaps advantageously in when angles fighting slow. Even the nigh useless flaps on the Fw-190,which don't help all that much fighting other planes, will come into play in close duels between two good sticks in 190s.
BTW, the instability problems with full flaps are entirely caused by auto-trim. The system attempts to trim the aircraft to fly straight and level at the airspeed you are doing in *clean* configuration. The extra lift of the flaps causes alot of nose-up pitch under those conditions. So either manually trim, or, if when entering flaps-heaving maneuvering, hold down the "I" key to turn off auto-trim and input alot of nose-down trim. (It is easier by several orders of magnitude to fight and shoot holding a little back pressure when the airplane is trimmed somewhat nose-heavy is to have to push the stick forward constantly when the trim tendency is to nose up.)
While I agree that flaps can be deployed at drastically low speed levels and they can help a most planes to turn tighter and a few plane a great deal tighter, it does however take that aircraft which in most cases needs speed to survive, to the other end of the spectrum and handicap them in terms of overall performance if the use of flaps is sustained. So again the case, at least in my opinion, goes back to the use of flaps as a major factor in %90 of air combat menouvers. Can those flaps be deployed at 250mph+? How many notches? What effect do flaps have at normal combat speeds?
Regarding the "combat trim". I alway have mine shut off unless in level flight on a long haul. There are a number of planes that can grab a few more mph if the trim is done manually. The Mossi being the first one to come to mind. Error in the flight model perhaps (naaaaaah)?
But even with the F4U's flaps deployed without "combat trim" on, it still needs a steady hand. It is planes like the F4U that will shine if the pilot has the skill. Some planes like the Spit16 shine regardless of who is flying it