I don't see 13/11 as significantly better than 12/12. I'm an Eldar player with mobile S6 weapons all over, AV11 gets toasted.
About 4 games ago my friend's Defiler took two penetrating hits (meltagun and rending ass cannon). Each rolled a 1, stunned. So, two penetrating hits did nothing to it.
If it gets immobilized, it fires the battlecannon still. If it then gets weapon destroyed, it still has a twin linked reaper autocannon.
If its 100% and gets weapon destroyed it can charge into melee.
I suppose from a Marine/gunline/lascannon spam point of view, the Pred is harder to take out. But from an Eldar point of view, or any team that would use mobility and lower strength weapons, the defiler is far more difficult to hurt, while I find it quite easy to draw a bead on Predator side armor and pop them.
Oh and I almost forgot, the fact that the battlecannon can pop Rhinos and other transports and a 6 on the ordnance table annihilates every passenger no save, very mean. Seen it happen a few times. No one likes losing an entire squad because of one 6 rolled.