I lose bagels to player's who are competitive in A/Open class, but for some reason want to play a couple of sets with me. I'm a slow footed 4.0.
I lose to competitive 4.0's in the middle of their tennis season, when I get to play once every two weeks because I windsurf in the summer. I'm a slow footed 4.0, worse, injured ankle, no running, just gimping around the court.
But double faults? OK, I can when I'm losing badly, trying to get off the court, but maybe once or twice a MATCH.
As a bad 4.0, I can place heavy lefty twist or top/slice second serves to your backhand, forehand, or into your body, 97% for sure.
That doesn't help me run to the alleys, cover short angles, and then cover lobs that land within 4' of my baseline when I'm at net. Nor does it help me hit my groundies into the 3' box I'm aiming at, 3' inside the baseline and 3' inside the sidelines.