Late war and early post war naval fighter aircraft from the US Navy were incredibly fast at sea level. These aircraft, the late model Corsairs and F8F Bearcat, needed a lot of engine power to takeoff from the carrier deck with an ever increasing payload of external fuel tanks, bombs and rockets.
The Me 109G you’re talking about is from 1943 and is actually one of the slower aircraft up that high, at least compared to American and British designs. An F4U-1A Corsair from 1943 would be doing 350 MPH at sea level. This is done with 2000 hp. The F4U-5 Corsair’s P&W R2800 would be producing 2750 hp at sea level. That increase in horsepower is largely down to improved fuel quality and water injection. All to allow the engine to cram in more fuel into the cylinder per 4-stroke cycle, without it exploding prematurely. It’s quite incredible the speed of technological improvement at the time.
Greg’s Airplanes and Automobiles has a great video about the F4U-5 Corsair over on YouTube. I will try to link it:
P.S. Unless, with “boost”, you meant supercharging and turbocharging. All single engine fighter planes had a form of super- or turbocharging since the 1930s. In fact, most WW2 combat aircraft would be unable to leave the ground without either form of “pushing” extra air into the cylinders.