Theories are not always correct. His game would badly descend if he changed his grip. A supreme player like McEnroe is not bound by hard and fast rules. Who makes the rules? People have said that if you do not have the proper style, then you can't run. But Zatopek was the radiant proof that this is not true. His style was worse than the worst, yet he killed himself when he ran and kept on winning. Previously, people used to say that you had to do the high jump in one way; now people do it an entirely different way. Previously nobody could imagine anyone playing with an over-sized racquet. They asked, "How will people be able to handle it? It will be dull and heavy." Now the theory has changed and most of the players use over-sized racquets. So styles are always changing.
Most athletes follow the general rules. But there will always be champions who don't have to abide by the well-established rules. From the very beginning they will rebel against the past and try to do something totally different, for it is their very nature to invent something new. Geniuses like McEnroe break out of the old boundaries and limitations. If they did not, everything would be fossilised and there would be no new creation.