There is such a thing as a repeating crossbow. The cartridge can be mounted above or below and the pull can be mounted above or below as well. Thus, for the volley of 5 shots which tends to be the limit of most high powered crossbows, with enough ships staggering their shots, it's actually one of the more plausible things.
However, without extensive ballistic testing, knowing the flightworthiness of the bolts as well as the range takes away from that. Moreover, it would take pretty extensive training not just for the guy "pulling the trigger", but also the crew of the Scorpion as well as getting the operator and the aiming/pulling crew in synch. Simple hand signals like that would make accurate aiming at 500+ yards very difficult as you need to be accurate in two planes and THEN include Kentucky Windage (aka leading the target).
So, while a potentially repeating Scorpion would actually be pretty reasonable and actually desirable (you don't want only one volley at a dragon), the implementation is very much fantasy. Not nearly enough time to fabricate, install and train the crews, both on the land based Scorpions and the sea versions which included the counterweight of a seat (of which the weight of the operator would change the operational characteristics of aiming the Scorpion) as well as knowing if such a strong force would affect the seaworthiness as they are so prominently featured on the bow. Being so high above the sea line as on the extreme bow would be a serious issue for the ship as well as its navigation. For as much power as those Scorpions had, they'd either have to really reinforce the bow making the ship nose heavy (not good) or risk the Scorpion ripping off the stem of the bow to the keel.
Still, the fantasy is fun to think about.
Also, the development of mathematics beyond astronomy was driven by trying to understand ballistics.
Also, prior to maybe 20 years ago, we didn't have working examples of trebuchet, just pictures. I forget which movie brought them back and figured some things out, but prior to that, it was all catapults (which are substantially more limited as a matter of basic physics). Pretty amazing when you think about it.