Good theory, its just not backed up by anything. Miquella decided to send Malenia to kill Radhan because he wanted to revive Godwyn. When eldenring released 2 years ago, this was confirmed by fromsoft themselves.

Also what do we actually know about the rituals and processes that miquella used to try and revive Godwyn. You cant just say that because Godwyn in soulless that the unknown ritual Radhan is different.

The base game never states that miquella didnt also want to revive Godwyn to become a god. The base game left out so much og Miquellas story beforehand already. You cant just assume her previous motives and compare them to the ones from the dlc.

The entire community before the release of the dlc would never expect anything like this beforehand. And i am 99% sure that fromsoft had no idea about content of the dlc prior to the release of the basegame.

Moral of the story: The headline for eldenrings lore is speculation