User blog comment:B214/Volume 23 discussion blog/@comment-82.178.103.238-20170802211752/@comment-10330822-20170807003534

Right, and Vali can't manifest Juggernaut properly at that point anyway. He is using his demonic energy to fuel the form, which is costly in a battle in the long run. So it makes sense that he can hold off Fenrir, but not defeat him, long enough that Arthur could use Excalibur Ruler on Fenrir.

That was the whole point on why the Empireo Juggernaut Overdrive is better, even if Vali is not manifesting the same amount of power as Juggernaut, like CxC, he isn't forced to waste his demonic energy fueling it.

So, the hypothetical complete CxC mode or a fully mastered EJO should be even better because they don't require anything to fuel them. So, in a perfect world, Issei and Vali would be able to manifest the full powers of Ddraig and Albion, without having to waste/risk any life force, santity, or demonic power to do so. Right now, they can't though, hence why they use things like Ophis's power and Vali's Lucifer powers to tip the scale to allow them to match dragons like Azi Dehaka and Apophis, who are on that Heavenly Dragon-Class level.

That is what I assumed the "stronger/better" aspect of the abilities was. However, B214 seems to indicate that was never present, which is odd, because I could have sworn I read that in the LN's back in volumes 10-12.