User blog comment:B214/Shin DxD 1 discussion/@comment-95.210.189.106-20180809123512/@comment-28884330-20180810025412

There’s no need for Issei to use True DxD. He’s only inferior to DxD L by a small amount since he’s still Heavenly Dragon-class, and he has Ascalon and Ascalon II, so he shouldn’t have much trouble defeating Crom Cruach. True DxD is not needed, and he even has Ddraig who can also defeat Crom Cruach.