>>58215405
Colosseum has the more difficult main campaign than XD. XD has a much much easier start, and the final boss can be cheesed with Shadow Lugia or Shadow Snorlax. It does not start getting to the same level of difficult as Colosseum until Gorrigan.
What you might have heard about is the post game/extra content
Colosseum has two Mount Battles, one for the campaign and one for the battle mode. XD only has a campaign mode Mount Battle. The CMB(campaign mount battle) for Colo is pretty easy, not a single fight is harder than the final boss of the campaign itself, as no one has Pokemon higher level than Evice's. XD's CMB is harder, having higher level Pokemon and better put together teams, giving the player an extra challenge after the campaign is over. I have not played the battle mode version of Colosseum in a long time, so I do not know if that is harder than XD's. Also XD has something called the Orre Colosseum, which is series of level capped Colosseum battles , that is likely the hardest piece of single player content in any Pokemon(that plays like the mainline ones atleast).
So XD does offer harder content but only after the main campaign, which is easier than Colosseum's main campaign.
