My personal take is that education bubble is driven by diversity. People will pay a lot make sure that their children are around the "right kind" of other children. The university system has found a way to provide this service in a way that doesn’t run afoul of the PC police. This service is therefore incredibly valuable.
As such, I don’t think there’s an education bubble. If there is one, I suspect that it’s in the bottom tier schools as the recommended article makes clear.