Scientific progress is not at all continuous and not systematically forward. There have been many periods of scientific regress. The most famous is the Dark Ages between Antiquity and Modernity, hence Luke's example of Hero.
But regress is all over the place, even in well-known examples of progress, like the Italian Renaissance. People often say that Renaissance art began with Giotto or maybe even so specifically with his invention of perspective. But, actually, most accounts of Renaissance art skip ahead a century from Giotto's death in 1337. In particular, perspective regressed and was reinvented in 1413 by Brunelleschi. And this wasn't even an independent discovery: Brunelleschi could see Giotto's work and knew that better was possible. *
Going back to Hero, "ancient Greece" is a bad category. Hero isn't the pinnacle of ancient Greek science, but a figure of a Roman era of rebirth after a dark age 150 BC – 50 AD during which we know the names of no scientists. In fact, almost everything Hero writes about he attributes to Ctesibius (d. 222 BC). If he is truthful about his sources, then there was a either a 250 year pause in pneumatics or there was more progress that was lost in the interim. In general, a controversial question is whether the rebirth in Roman Alexandria reconstructed and surpassed Hellenistic Alexandria or whether it was only able to understand a few books.
* Lorenzetti (d. 1348) seems to have been pretty good at single buildings, but bad at putting them together. Compare the only city I can find by Giotto.