Getting glad might be easy for players like us, but what in the game is more difficult? Raiding? Lol.
I hope your not serious. So many encounters have been way more challenging. There has not been any season where I could not reach Gladiator in 2-3 days of playing with some downright dumb setup. May it be TSG, 4 DPS, Doublehealer, Beastcleave, 2xMelee + WF totem.
Getting rank1 is something else, but Gladiator (atleast the lower ranked Gladiator teams) is in no way a hard Feat of Strength to accomplish - more a class based Feat of Strength (a cool idea could be to reward the top 0,5% of each class Gladiator!!).
On the other hand, wiping 3 months on Lich King HC, Cthun, Muru, 4Horsemen, Spine HC, H Ragnaros all before nerfs, fucking retarded.
But in all honestly, comparing PvE to PvP makes no sense (1 enviourment being static, one being dynamic), but if you insist to try and go down the path and still argue which one is hardest, obviously just look at time spend on either.