What is going on here? When you’re between levels 80 and 90, you can run either Cataclysm or MoP dungeons. MoP dungeons are difficulty appropriate - or easy, rather and are for the most part, smooth and quick runs. Cataclysm dungeons, on the other hand… there are some notable dungeons that hit hard, have terrible checkpoints, and force near or full wipes on a single missed mechanic. Throne of the Tides, Grim Batol, Blackrock Caverns to name a few tend to go, “Hey, you didn’t pay attention. Now you’re already dead!”
Hope you get veteran players for Cata dungeons. Pick MoP dungeons for a much better efficiency with EXP and time.