It is a great defensive tank for its size/weight/cost in either version. The only reason to build a Scorpion vs a SFE Stingray is you can't handle building/maintaining the engine or the L-PPC on the Stingray. The SFE Stringray at least ties in capabilities, is close in cost, and much better in logistics compared to the Scorpion.
The reason tanks like this don't replace mechs across the board is I can spend 6.5m c-bills and build a 35 tonner going 8/12/7 with a ERPPC and TC, XL, Endo, and 6.5 tons of FF that is more maneuverable, with a bigger punch at a better range. The 26 Stingrays defending vs 4 (more or less even c-bills spent) of my quick mech builds attacking are most likely to win in a single, stand up fight. The thing is the mech lance can go in water, jump over canyons/forests etc, basically they can go a lot of places the tanks can't go, so they don't need to get into a stand up fight outnumbered like that. The mechs are going to pick a fight, take out the tanks they can, leave and do it again tomorrow. This leaves out things like the difference in logistics footprint, dropship deploy ability, the need to cover multiple potential raid spots, and so on that are purely in game concerns.
If my choice is 6 Stingrays or 4 Locusts I'm taking the tanks for anything defensive, and most larger assaults. If it is 6 Stingrays or 4 Locusts for a planetary raid the Locust become more appealing. If the choice is 50m worth of Stingrays or 50m worth of whatever I want the little tanks may still go high in a defensive scheme, but wouldn't have a place in many other battles.
I hope this did a better job of getting what I was trying to say across. I really like the Stingray, and would definitely expect to see it as a very common in universe vehicle in an era where L-PPCs andSFE/XLs are militia grade equipment.