All he was asking was for a WHY they seemed to hit so much harder... No reason for the crass and rude responses, guys. o.O
Anywho, yes, OP, like everybody else that bothered to respond to your question said, they hit harder, are a higher level, and have more help. I highly encourage you to have every single person in your party in Vent (or a similar program) so that you can accurately plan cds ahead of time.
The best way to get through a challenge mode is AOE stuns. Every class now has a talent point that allows for this. The Monk ability is in Tier 4, I believe? The Leg sweep. I also highly recommend that every person in your party also grab their AOE Heal ability, as most classes have one. Yours is in Tier 2, Chi Blast, perhaps? Either way, by rotating these cds, it not alone helps with survivability, but also ensures that people are less likely to die.
The stuns are the #1, though. The less amount of time that they have to hit you, the better. So, for instance, you pull the entire group, you hit your AOE stun - 5 seconds later, they start hitting you again, you pop your mitigation, 2 seconds before it drops off, it's now DPS1's turn to pop his AOE stun. Then DPS2... and so on, so forth. At the same time, you're also rotating the healing cds.
You also might find yourself actually doing a better job with a Disc Priest or a Monk Healer, mostly because they do damage to heal. The more damage going out, the faster things are dying. That's why so many Gold holders actually did NOT bring a healer to their Challenge Mode runs. The extra dps was just too important.