Testarossas

They're both smurfing!

"Before I dreamed of existing"...

The Devils have Sirzechs, I don't need to explain that, they have Ajuka, he's just plain scary to have as an enemy, he'll plan and research you to death, he's also stupidly strong, there are other Satans as well. The Fallen have Azazel, he's a bit similar to Ajuka, if weaker, and there's everyone eles in their faction. Then threre is Heaven, they may not be as strong as the Devils faction, but they have God's System, if another Pantheon or more really pushed them, they could probably use the Divine equivelent to a Nuke with it. There are more reasons, also, fighting against the Biblical faction would do massive damage to whatever enemy force it is doing it, possibly allowing others take advantage of that.

According the story, Erik was born in year 982. Also, according to the HP Wiki, Merlin was born in the year 982... Well, it does have parentheses for "or later" too.