The 'catch up' dungeon was a commonplace design in Wrath of the Lich King and Cataclysm, one that's fallen out of favor in Mists of Pandaria to be replaced by the Timeless Isle and Raid Finder. It's understandable that this should be the case - designing a dungeon or dungeons is a lot of work, and it means other content (like, say, an open world zone like the Timeless Isle) won't be delivered. And as a catch up mechanic, the Timeless Isle is in many ways superior to a five man dungeon. Art assets were reused and gear randomized - you get a piece for your class and spec, but it's not necessarily ideal for them, so there's benefit to keep farming the zone. Furthermore, there's an upgrade mechanic in place (Burdens of Eternity) that will allow you to make pieces that are much closer in quality to current raiding, giving you even more incentive to keep running it.
However, I'm much more a fan of the catch up dungeon. As much as I like exploring on the Timeless Isle, there comes a time when you've explored all that you can, and the Isle stops having any use for you. Even for a dedicated alt-maven, it's lack of weapons (yes, I know you can get some weapons, but even after the upgrade in 5.4.7 they won't be very good) at a reasonable cost makes it less appealing to me. The Timeless Isle trades the random drop factor of catch up dungeons for near certainty - you will get every piece you want, eventually. It's an efficient and workable system and I dislike it. In comparison to Wrath and Cataclysm it lacks in the following areas: