User blog comment:B214/Volume 23 discussion blog/@comment-82.178.103.238-20170802211752/@comment-10330822-20170805120529

I don't have access to the quotes, but you can read the articles on Juggernaut Drive and Cardinal Crimson Promotion, and it makes it very clear.

"The Juggernaut Drive...temporarily unleashes the full power of the Heavenly Dragons sealed in the Sacred Gear, but at the cost of the user's life and sanity."

And then the Cardinal Crimson Promotion article explains "Cardinal Crimson Promotion incorporates all three Evil Pieces traits, making it the most balanced and most powerful form of Issei's Scale Mail. The Cardinal Crimson Promotion Issei's answer to a power different from the Juggernaut Drive after successfully overcoming the curse of the Juggernaut Drive, making it at least as powerful as the latter. This form, however, is still unstable and consumes too much energy rendering it uneffective for long battle. This form also requires mastering the three forms of Illegal Move Trident in order to stabilize its powers."

In other words, Juggernaut Drive = Ddraig's "full power", while Complete/Stablized CxC Mode = Juggernaut Drive.

Hence a Complete CxC Mode would also equal Ddraig's full power. Meaning Issei would be at least as strong as Ddraig.