User blog comment:B214/Question and Answers 6/@comment-2607:FB90:603D:5340:4082:7A47:2AEA:26C5-20190115200556/@comment-37165251-20190116190402

While it is true that Regulus may not be in the Powerclass of Ddraig and Albion, the Power of the Spirit in the Sacred Gear is only one Part here. Never Forget that Sacred Gears are changing...if not we never had five new Longinus.

On the other Hand there is Sairaorg. He himself can become incredible Powerfull (ok he already is, and is for Devils still very very young). So with Sairaorg becoming stronger and becoming in Sync with Regulus he can reach a extreme Power.

Hey I mean we have a HUMAN that is soo strong that he can theoretically kill Gods...which means he uses hith Longinus to the fullest...I speak about Tobio Ikuse. I mean killing an Executive Class Grimm Reaper, who is a Half-God that would be theoretically even or stronger than Maou-Class Devil, is an incredible feat for a Human...also not forget that like GrimReapers he can Cut Souls (ok not Ophis, Great Red and Issey^^).

So to put it together, Can Sairaorg become as strong as a Heavenly Dragon...maybe, but I think not we will see it in the Light Novels for the next time.