Why is outlands that hard/bad to level in?

Personally i always cried myself trought 50-58 then jumped with joy once i hit outlands! Boosted my paladin from 58-60 in 3 hours with a 70 friend warrior helping out! i guess i could have done it pretty fast with good gear!

My first goal once i hit 60 will be to get the trinket with spell damage and critt since he should be doable with 5 ele shamans!