Anyone who scales to Soul Edge is planet level, since Soul Edge can only unleash its true potential when changed into a form that suited its wielder. The same Soul Edge that created the Evil Seed, which was stated by Zasalamel to be capable of destroying the planet. It should be noted that Soul Edge/Calibur themselves are capable of oneshotting an Azwel who became far stronger than even that. For that matter, the Conduit being capable of reaching into the Astral Chaos to even wield one of the spirit swords would have to be > the Evil Seed itself. It should be noted that the Conduit scales to everyone in the cast, and is still below the likes of characters such as Nightmare and Zasalamel. It's also canon that Siegfried managed to defeat Inferno all the way back in Soul Edge. Hell, even literal nobodies get scaling from the two swords if Chronicles of the Sword is anything to go off of.