User blog comment:B214/Volume 23 discussion blog/@comment-77.188.220.109-20170502203809/@comment-30048084-20170504195152

@anon In order to wield a holy sword you require the inborn ability to wield it something Xenovia possesses and did not lose it when she was reincarnated that is why she can still use holy swords. There are artificial holy sword wielders but they are incapable of wielding extremely powerful holy swords.

Issei was not born with this ability and was not given it, the rituals in question were to prevent Ascalon's aura from 'attacking' Issei even then it had to be fused with the Sacred Gear. Merely being in the presence of a Dragon Slayer causes a reaction in dragons where they can sense their 'desire' to kill dragons.

A weak mind? How so?

was it when he used the Divine Dividing's own ability against it to destroy the armour during his fight against Vali in Volume 4.

When he used Flame Blaze against the wielder of Night Reflection that was untouchable from normal attacks noticing that he reacted to the heat of Kunou's fox fire in Volume 9.

where he remembered that Cao Cao had implanted one of Medusa's eyes to replace the one Issei destroyed and used Samael's poison against him in Volime 12.

You keep on stating he is weak but you ignore the fact that a large number of characters without their Sacred Gear would be incapable of fighting even a Middle-Class Devil. Issei is capable of fighting multiple magicians at once without the Boosted Gear because he is capable of Dragonification an ability that no other character can do.