User blog comment:B214/Volume 23 discussion blog/@comment-1359322-20170318060342/@comment-10330822-20170319041016

Exactly, Issei needed 4 of his pieces mutated to he could use the kind of power to face something like the top-tier Longinus. Had someone like Cao Cao, Dulio, Leonardo, or Georg been found instead of Rias, she probably couldn't have revived them.

We also know this since Heaven needed to use a Joker card to reincarnate Dulio as an Angel, because he was a top-tier Longinus user. Joker cards are like the mutation pieces of Brave Saints, with no set number or suit. Chances are, just like with what we saw with Issei, they couldn't have reincarnated him with anything less.