Yes many did cope with the additional torque of the Merlin however many didn't even back in the 40's and 50's.
A big difference between now and then is that military pilots didn't buy their own way onto high performance single seaters.
RAF military pilots of the 1940s were streamed into single seaters or multi-engine during basic flight training on Tiger Moths or Magisters, with single seat pilots going on to Harvards and multi-engines going on to Ansons. The fact that high performance single seat fighters could be a handful was well recognized and those who it was thought wouldn't hack it, were weeded out very early in the proceedings. Of those who made it all the way through flight training, only those with the best responses and finest control touch went onto single engine fighters. Even then many were 'chopped' from the course and never reached a squadron.
This policy remains in place to this day. Fast jet jockeys and 'pie eaters' are sorted out very early in the training process. In today's civil environment, if you can afford a part share in on old 'warbird' you can buy into the training to fly it and there's no 'chop' in these circumstances. Its a fact that not everyone has what it takes to fly a single seat fighter aircraft - vintage or new.