Of course, that parabola can begin later rather than sooner. A hard slider has a relatively short "parabolic path". Also, the researchers didn't seem to bother much with the knuckleball, which can indeed "break", sometimes more than once during a single pitch.
Besides the knuckler, they also didn’t look at a good split finger fastball. Those thing drop right off the table up at the plate.
Freegards
A hard slider has a relatively short "parabolic path".So do some changeups, such as the ones thrown by Sid Fernandez, Frank Viola, and Eric Gagne, to name three with short parabolic paths and murderously-timed breaks that I've seen.
Biggest breaking curve balls I ever saw: Sandy Koufax, Bert Blyleven, Dwight Gooden.
Strangest slider I ever saw: Roger McDowell's, probably because he was primarily a sinkerballer and even his sliders tended to sink as they turned.
Single nastiest curve ball I ever saw thrown: The little curve Sid Fernandez threw in relief in Game Seven, 1986 World Series. Oh, he was bringing the heat (he opened the top of the fifth by literally blowing Jim Rice away on three straight swinging strikes---which may have been equal to pulling the mask off the old Lone Ranger, considering that Rice was, even on his downslide, a first-ball fastball hitter and a deadly one if the fastball was meaty enough; Fernandez relieved Ron Darling in the fourth and ended up with four strikeouts in two and a third innings' relief, before the Mets tied and went ahead in the game), but he dropped strike three in on Spike Owen with a nasty curve ball that didn't even have much of a break---and he threw it so deceptively, with that lunging-forward motion of his, that Owen just had to be thinking the fastball was coming at him . . . and plink! it broke like a floating soap bubble, a real tiny arc, and landed dead center in the zone. Owen probably needed smelling salts when he went back to the dugout to get his glove . . .