Although some of my favorite civs have a great siege department, I realized that I barely use scorpions. I also hardly ever encounter any and as far as I know, this unit is not popular at all, no matter which elo.
There might be many reasons for this. My suspicion is, that scorpions have no real role. They cost something close to 2 archers, but - considering their fire rate - have a weaker single target dps, are not effected by ballistics and, are too slow to micro or kite and take much longer to field, since it takes ages to go to ca and build siege workshops. The only argument for them is the splash damage. Anyway, for that role, players prefer the mangonel, since its damage is significantly higher.
Ofc a buffing scorpions could increas their popularity, but I don´t think, that this woul be a good idea. A buff to scopion would most likely lead to the result, that either mangonal gets pointless because of better scorpions or the result would be 2 units with nearly same quality an purpose, which would also be a little bit odd.
Maybe, it would be better to give scorpions the concept and role, they really had: Scorpions were designed to fire spears/bots or stones on sigle targets over a high distance (much higher than archers were able to).
Maybe scorpions should work just that way - A siege unit, with a good range (something between mangonal and treb), with quite a low fire rate and just against single targets, but with fast moving missiles (like an arrow) and heavy damage. (ballista worked that way in AOE 1 as far as I remember and was a great unit there. Balista also worked that way in Stronghold and even there it was good).