Merlin not calling himself a Grand in the story says otherwise, especially when it's relevant for him to do so.
No, you're the one ignoring what the story gives us to parrot this theory, as if it means anything. So no, get the proof from the story, and don't wave around profiles without considering any shred of context.
This is mighty rich coming from the guy who thinks beating up on the Bel Lahmus is decent enough to show that Merlin is a Grand.