The Mosquito is not fixed. Having tested it, and the Spitfire Mk VIII, there is either a global bug causing all aircraft to be faster than they should be or a global bug causing air speed to be reported as higher than it is.
I reached 367mph on WEP at 200ft in the Mosquito, up from 338mph in 2.17. I reached 362mph at 200ft in the Spitfire Mk VIII before auguring it intentionally. It also had a top speed at that altitude of 338mph in 2.17.