I don't think stalling a part 121 passenger carrying turbo prop is a "mistake". A mistake is dialing a wrong frequency, a wrong inbound course, a missed fix in a flight plan etc...

I think the issue is the airlines' (especially the regionals) tendency to push people through training who don't have the necessary stick and rudder and/or judgment skills to safely operate a complex aircraft. I've seen it with my own eyes numerous times as a former regional guy.

I'm not necessarily saying this particular crew was skill-deficient, but the scenario does point that direction.