I'm not sure Handel saw it at the time as "good fortune" that the employer he had deserted in Hanover should pop up as the new king of his adopted country only two years later. It turned out all right in the end, but Handel had to work hard to get back into the king's favour - the "Water Music" was part of this charm offensive.
Not only is there not a definitive recording, there is not even a definitive score of "Messiah", as he wrote different versions of some movements for different performances (and even replaced some completely), to make best use of the soloists available for each one.