He was blindsided by what the results would be and therefore didn’t think things through. My friends are so amazing they can handle anything and im the master of chaos so I can be the perfect safety net if anything goes wrong.
That’s kinda how I look at it. There’s a potentially interesting idea for a gambit in there. He gets these villains to team up. Maybe working together teaches them about friendship and they reform themselves. Maybe Twilight and her friends reform them. Both the audience and Twilight get a climactic final battle either way. I’d like to think that’s the intent, but there’s a lot of tissue missing, so I don’t think it works. Discord consistently screws up even the most basic tasks, so I have a hard time believing that’s he’s suddenly playing that kind of 4D chess.
I think the problem with Discord as a whole is that he’s Diet Chaotic Neutral instead of Full Chaotic Neutral. Good examples of CN done right are Captain Jack Sparrow or Rick Sanchez. They might save your life; they might screw you over. They have their own agenda: maybe you’re part of it, maybe you’re not. The bottom line is that they have the mojo to almost always be in control of the situation. That would have been a more interesting version of Discord. Some days he terrorizes Ponyville for his own amusement, some days he plays Ogres and Oubliettes with the gang. A “Go Karting With Bowser” kind of deal. He’s just “like that” and completely owns it.
Both the premise and the gambit angle would have worked if Discord was characterized like that. Discord miscalculating and losing control of a situation should mean something.