Thordan Ex would very easily above Coil difficulty, if the DPS/Enrage check were even slightly less forgiving. So, yeah I'm not surprised a lot of people are struggling with it, a lot of folks never stepped foot into Coil, and were never challenged like that. <_<;;
Edit: To be clear, mechanically it's more difficult then T13 I think, there are more mechanics and they come more quickly. T13 hit a bit harder (at the time,) and the DPS/Enrage was very much real. So it was a lot less forgiving of mistakes. Net result is that you can make more mistakes in Thordan and still get your first clear, making it easier to learn overall.