Re what Borg said, that's double speaking! Or speaking out of both sides of the mouth.
If you constantly need to cater to so called proper percentages -- which is halfway controlled by your opponent -- you really have no/little say in your consistency. For example, against someone good at defense like Djokovic (recreational Djokovic's) you WILL BE FORCED to make very low percent shots. Where's your consistency now?
I know this. My friend who has very good work ethics, loves exercise and would try to run down as many shots as possible. Normally I can put away balls that land in my service box against other opponents, but against this friend, I really have to topspin it hard and closer to a side line, which greatly reduces my chance (consistency), but no choice or he will get his racket on it and likely win the point with a lob or passing.
Nadal doesn't want to hit the ball out, doesn't want to take unnecessary risk if he doesn't have it, but the fact is he did hit out, ALOT against Djokovic, and lost. Why? does he suddenly abandon his consistency? I doubt that. He is forced to make very low % shot out of necessity (and still not enough and lost).
Borg's advice is sound. It doesn't mean that you're going to beat everyone. If you need to make low percentage shots to counter your opponent, chances are that you're going to lose anyway. Very few players are going to win a match where they repeatedly have to make low percentage shots.
There are limits to every strategy. Borg himself was the Djokovic of his era...someone who could run for hours and get to everything, frustrating his opponents. However, he eventually met his match in someone who was the opposite...JMac, a supremely gifted S&V who imposed his game on Borg as the match went along. More than the style you play (baseline/grinding vs attacking), the person who usually wins is one who can impose his strengths on his opponent as the match goes along.