Is it feasible to assume that a graphologist would be able to undertake a comparative analysis of two scripts, one handwritten in a journal in regular sized script while the other was writ large with paint, daubed with a paint brush onto stone?
Moreover, is it likely that there would be similarities in stroke formation between lateral ink-based writing in a journal and when one is daubing paint onto stone "vertically"? - which is admittedly unnatural for a person who otherwise always writes laterally.
Perhaps the gang left their graffiti, knowing that the 'roof' was going on and that the relieving chamber was to be sealed. The script did not need to be either neat or tidy because the scribe assumed no-one was ever again going to see his handiwork: he just felt the need to announce that he had been there, part of the construction. Isn't that why people of all cultures across history have always graffitied structures?
It is only because of 19th C explorers blasting their way through with gunpowder millennia later that we are even aware of this graffiti in the relieving chamber.
By the way, vertical inscription was a perfectly normal hieroglyphic convention; there is nothing at all unusual about this. Also, the "ducks, birds or whatever they are" are quail chicks which give the 'w' or 'oo' sound to the name in the cartouche - Khufu.
I agree with your sentiment that the opinion of an independent arts professional or a graphologist should be sought.