User blog comment:B214/Question and Answers 6/@comment-207.242.44.6-20190815185621/@comment-2806:108E:1E:1D9C:5183:A549:91F0:1E07-20190910011714

Well, scale mail is the normal power of Issei's longinus. Issei with his longinus in balance breaker can only achive a power that will increase as his base power increases. And for Issei to unleash full power of Ddraig, his only way to do it is with jugguernaut drive which will take his lifeforce since he has little aura.

With his Triana, Issei combines his power of devil which are the pieces inside him with the power of his longinus, which enables him to unleash the full power of triana without the risk of losing his life, yet, as before, he needs to train all his forms and his base form.

True Queen is meant to have the full power of Ddraig, but Issei needs to be OP to unleash that power, IMO he has to have Satan Tier powers in his base for his true queen to have the full power of Ddraig.