There are some funny reactions and even arguments in which a few fans say that Cozy Glow is redeemable, that the authorities were too harsh by capturing her into the Tartarus and that they left no room for her.

Well, guess what, you had a filly in the past that was selfish as well but she didn´t harm beyond a certain group and saw how her actions had consequences: Diamond Tiara. Even in Flight to the Finish, she had to use the crippling argument to make Scootaloo feel bad and when that happened, DT was insecure about doing it because going into that route passes the normal limits. Not all the times she was that bitchy with CMC (Twilight Time) and her actions only put her class at her service (Ponyville Confidential) but after that, she was getting more infamous and that´s why Pipsqueak won the elections in Crusaders of the Lost Mark, with Silver Spoon´s vote behind him.

What I mean is that she knew the limits, she did have a room for feeling remorse about her actions and got redeemed because she figured out what her problem was with the help of the CMC.

Here, the process is in reverse. Cozy Glow has had all the friendship lessons in front of her, she learned all of them and became an exemplar assistant/student for the school, to the point Twilight relied on her even for the equipment for going to the Tartarus. She was a reference for the entire school but all of that was a slow process, they all were a means to an end.

Pretending to be fine by studying all the concepts of friendship to twist them, gain friends (more like gaining an army of ponies) in order to become the ultimate leader....but she doesn´t know what to do with it. However, the manipulation went very slowly in a seemingly innocent way. It´s beyond the usual level ordinary of politics the skill of manipulation she has offered in this finale. She was going to show it sooner or later, but the execution just crosses a black zone. No wonder other fans whitewash all the other villains in comparison because sweet mother of Celestia, some lines sound like she is a renegade of the society when she has had all the facilities and skills to apply them correctly.

The analogy is that those lessons give power. Nonetheless, this is like using a knife: either you use it to cut food or you use it to kill people; or chemistry: either for medicines and industrial products or for making drugs and nuclear weapons. It´s up to you to decide what to do with that knowledge. That´s the final result with friendship, the actual concept pushed in this show. What´s worse is that by her being a pegasus, all the ponies betrayed Neighsay and the ones who rescued him were the subpar creatures he had feared.

In contrast, there were other 6 students who were taught with the same lessons that Cozy learned during this season. Just that we knew their development, where they came from, how they act together from the start and how over the time understand what the concept of friendship is with different experiences. The finest example for it, besides School Daze, is What Lies Beneath, in which they prove how to overcome that challenge from the Tree of Harmony itself.