User blog comment:B214/Question and Answers/@comment-50.11.177.49-20130708052828/@comment-16075832-20130716183719

True, plus Vali mentioned in Volume 12 that his Juggernaut Over-Drive could be strengthened further which implies that Juggernaut Drive has a set power level. The same is likely true for Issei's Cardinal Crimson Drive. Though, the Juggernaut Drive does give him access to the Longinus Smasher. Maybe it will become usable in CCD in the future.