Sampras said, "I turn my shoulders, I bend my knees and I put it on the line.", and that's all he thought about. His toss was never off at all. His rhythm either. Takes more than hard work and reps. The coil needed is extreme.
The speed vicious.
Even if you know all that, just try to go and do it.
The odds are high you will fail forever.
That's why pitchers and big servers get paid so much.. They are rare. Sampras contact was often three feet inside the baseline. Just try that once. He and Becker bent their backs way forward to get more into the shot, and a better angle into the court. More pathway to create speed and mass. Their forearms snap over, not the wrist. Even if you work on it for years, you will be lucky to have one unbreakable game in a match. Sampras would hit about 100 serves a day. Lubijcic would hit them for an hour a day. And how many out there hit ten for a practice warm up?
AS you can see, every one pictured here uses a platform stance, not a pin point.