User blog comment:Piyush Banerjee/Shin DxD 2 discussion/@comment-37165251-20181219151825/@comment-28884330-20181219173427

No mention of surpassing Sirzechs and Ajuka has ever been made, even though Balberith's case specifically implies it. And this is the quote on Dragon God-class:

"As for the Super Devils, the female was named Verrine, while the male was named Balberith. Hades looked at the man — Balberith’s image.

<<…Number 61616 Balberith. A monster exceeding all specifications. I never imagined that someone potentially capable of challenging a Dragon God single-handedly would be born…>>"

As you see, Balberith is singled out, and there's also the mention of "potentially", so he's not necessarily at that level yet.