Well, the fact that it was used in so many theatres shows something. It also shows that the long range escort of bombers operating out of Britain was just one tiny part of the air war.
And the Spitfire did not have such a short range. Not once they started equipping them with drop tanks and extra internal tankage.
Most of the Spitfire range figures are for high speed cruise, not maximum range cruise.
Here are Australian tests of a Spitfire VIII, fitted with a 90 gallon drop tank, carrying a total of 213 gallons of fuel:

(Whilst it says "ferry condition", it's with full armament and ammunition)
Use 20 gallons warming up and climbing, 30 gallons in combat, and at 283 mph cruise you've still got a radius of 500 miles, with 170 miles in reserve.