>letting four earth ponies escape
They're nice ponies. Them stopping to make sure that Daring Do is alright is entirely in character for them to do, even if it means the bad guys get away.
It isn't the tactically optimal choice, but it is the empathetic choice, and it isn't as if they always make the smart choice. Plus, Rainbow Dash wanting to hang out with Daring Do trumping taking off after the ring is entirely reasonable, and could be a further reason for annoying Daring Do - they could have stopped them, but instead stopped just to bug and fawn over her.
>flies in the face of everything I've ever read
Quite the opposite in my experience; most guides I read about DMing warn explicitly against this very thing. In the end, it is very important to remember that the focus of the story is ultimately on the actions of the protagonists, i.e. the players, and not on the villains. Yes, the villains are what allow the story to exist, antagonists give the protagonists something to struggle against, ect. but part of the joy of RPGs is that you can, in fact, catch the villain monologing - and that's -fun-.
Trying to show off how awesome your villain by taking away player agency is a big mistake and alienates your players and detracts from their experience. Agency is important in RPGs, and it is the high degree of agency possible in such games which is so attractive to many players. Sure, some players are perfectly fine with what amounts to cutscenes in games, but most players play in games in order to participate, not to stand back and watch the DM roleplay. This is why people recommend against just having something happen and not allowing the players to do anything about it if it takes more than a few seconds. Obivously it depends on the particular group but as a general rule, having something happen like what happened in this episode isn't a good idea in RPGs. I've found that if you go more than te