I could deal with the time-traveling. I could deal with the sorceresses possessing other sorceresses to release certain sorceresses from prisons. I could deal with the surprise that they all coincidentally grew up together in the same orphanage and that they were besties. I could not deal with the amnesia revelation. It could have perhaps been somewhat viable had they not immediately blamed the GFs for the memory loss. If anything, a more interesting plot twist would have been perhaps some sort of quest or route in the story leading them to find what exactly caused their memory loss and OH tit GFs, REALLY? But the way it was all pretty much instantly decided after realizing they had lost their memories felt like a cop-out.

A better way to make it more plausible would have been to even mention little things about memory loss earlier in the games, like when reading through the tutorials and computers in the Garden - maybe articles about students complaining about memory loss or students mentioning it when you stop to speak to them in the halls once in a while. Jumped the shark there, indeed.