Well he was able to adjust his game at Wimby.......he worked to improve his serve in the mid 70s and it became a weapon after 1976.....he always had solid volleys (he did fairly well in doubles in his early career and in Davis Cup) and if you watch the old matches from 1976 on at Wimby Borg didn't just stay back but attacked the net when it counted.
Also the key at Wimby for Borg was getting thru the early rounds, he has some huge scares in 77, 78 and 79 in the first week of the Toury and much of it was due to the grass. The early week the courts were fast, slick and in great shape by the 2nd Monday it's looked like clay courts on the baseline and the balls began to bounce higher and slower.
As for Paris it's simple......BB was the greatest clay courter ever and RG was his baby. He could park himself at the baseline an no one could touch him (except Panatta who was the only guy to attack BB on clay and win). If Borg had stuck around he could have won 10 RG's in a row.