What in particular is your problem with cartouches in general?
In general: the assumption that a cartouche contains a royal name, because that's what the Chinese did.
In 1761, before Champollion began translation, Barthelemy wrote that the Chinese put royal names in a rectangle. This was echoed by Zoega and Ward. Armed with this assumption, Champollion tackled the cartouches of Ptolemy and Cleopatra.
This first assumption, based on a Chinese tradition, was the crucial factor in Champollion's progress. There are many exceptions to the the cartouche rule; royal names without cartouche, non-royal names within one.
I wonder why the AE's would take up a Chinese tradition.
The Abydos list is a deep deep subject. Did you know that Champollion was taken to task for "falsifying" it?