On Elidibus's Nature:
Elidibus is a primal. Okay, that makes sense. He was basically tempering the people of Norvrandt in 5.2, making them think and act like warriors of light, after they saw a starshower.
And ... wait a minute. There have been theories going around forever that we are immune to tempering because Hydaelyn got us first. But what if Elidibus got to us first? We did, after all, first start acting like the Warrior of Light right at the beginning of the game, after seeing a star shower...
And On His Actions:
However you look at things, this was not a victory. We slew hundreds of heroes from different worlds; likely leading to even greater loss of life and a much freer hand for the remaining Ascians. It's possible that was his real goal; he just wanted to make sure we were strong enough to 'kill' him (along with the very strongest of these heroes) and then make the standard Ascian escape.
Even more terrifyingly, while it seems like he didn't know the Crystal Tower could end him, it's possible he knows more than G'raha does, and that Elidibus is now in full control of the tower.
Alternatively, it's also entirely possible that Elidibus knew everything, and wanted to die - but couldn't achieve it any other way. Making things even more tragic.