I still haven't given up on finding the 106 minute version. God only knows what could be in those missing 19 minutes. Presumably, Sofia Dionisio's performance is there as she is nowhere to be found in the shorter cuts.
Indeed, the handling of Bannen and Finlay's characters, and the lack of any good explanation for why the women give themselves to Satan, are among the film's chief flaws. I believe Carpi's original novel could have been fascinating to read and do a comparison to the film but I don't think it's ever been published in English.
As for the lack of any magic powers on display, I think this is due to a low budget that didn't allow for any special effects. The only notable effect is when Lara Wendel uses her hand to burn that geeky boy's chest and that's done mostly with make-up. Then there's rather idiotic scene where Marisa Mell (who seems to be the most faithful and powerful of the withces) tries to intimidate Wendel by vanishing into thin air and then appear in a different place in the room. But I hardly think this deserves to be called a special effect - it's simply an old-school cinematic trick that can be achieved by anyone with a camera and a tripod to keep it steady.
