People need to learn the difference between "hard" and "boring".
1. Does the bosses take time to kill - yes.
2. Are they hard to kill? - no.
3. What's the requirement - skill spamming that consists of DPS and a cleric.
^ That summons up the current dungeons. Now if we wanted it to be hard, and exciting, challenging, we wouldn't be able to skill spam. The reason why the mobs can't turn into more of a challange is because all of them do the same thing. You kill a spider, but it's not that exciting, some of them maybe stun, while others debuff you or what ever fancy skills they added to those mobs.
For a real challange you would need things like:
Ulvrick throws nets on the ground, if you step on them by accident, you'll be stuck til "x" person does this to get you out / limited to a certain amount of seconds where you aren't allowed to skill or get healed while trapped in this net.
When the monsters huge laser (or what ever it is) Swooshes by the room, people have to run away a bit not to get hit by it , otherwise it leads to [insert some dangerous action here].
^ That's really bad examples but you get where I'm going. For it to be a challange, you have to have certain tactics, and know when things happen and how to avoid them, right now there's no such things in dungeons, only if you're unlucky mr. ulverick will pour all his negative stuns on you.. but more than that doesn't happen. Let's face it, it's not difficult, it's time consuming and boring, there's a fine difference.
Also, for those who want easier modes to clear the dungeons in seconds instead of spending actual time on playing the game, don't expect to get fancy rewards in easy modes and normal modes, the things you want - that you now call "bad rewards" would be in the hard modes, what says the reward would be the same just because they change it into easy / normal / hard mode? - The reward you get now would be at the hard mode, so technically you wouldn't play easy mode - would you?
But I do agree of the whole idea between different modes for ungeared people and such to be able to gear and maybe get rewards to be able to join the more difficult dungeons in the future, only for the reason that it actually costs a lot of energy to enter these dungeons, you wouldn't want to waste that energy and wipe during the whole time.