The only part of Shattered halls that was hard was tanking. I knew so many tanks that were successful in vanilla that couldn't do a 45 minute shattered halls run for the life of them, but I could do htme with no CC on my alt without much trouble. It was a fun dungeon for sure, but it was only hard because of the limited toolset of the warriors of the day compared to what the dungeon was throwing at you.
Challenge Modes aren't that kind of 'unfair' hard, they're coordination among everyone, I have equated them to BC heroics at launch in appropriate gear except with a timer. I stand by that, Shattered Halls was tank-heavy, but overall the original BC heroics were challenging and required a lot of tricks for your group to enable tank survival. Challenge Modes totally deliver on that, anyone pining for BC heroics - there you go, make a group. Oh you wanted to queue for them? I thought you remembered BC where you had to actually make one because you wanted to have a snowball's chance in hell of success.