The long reigns
Kings reigning 28,800 years prove a non-human dynasty.
The King List uses a sexagesimal numeral system and a political purpose: to make scattered dynasties look like one unbroken succession. The long reigns shrink to plausible lengths after the flood.
The arithmetic
Run the antediluvian figures through base 60 and the pattern is immediate: 28,800 is 8 sars, 36,000 is 10, 43,200 is 12. None of them is an odd number, none carries a remainder, and none looks like a record of anything observed. They are round numbers in a system where sixty is round, chosen for magnitude rather than accuracy.
The gradient after the flood
Immediately after the flood, reigns of a thousand-odd years appear; a few dynasties later they are running to twenty and thirty. By the first dynasty of Ur the list can be cross-checked against inscriptions and broadly holds up. A dynasty of long-lived visitors would not fade politely into ordinary chronology — but a scribal convention for 'the deep past' would, and does.
What the list was for
The document's purpose was to argue that kingship is singular and transferable, so that whoever held it now held the only one there had ever been. Inflated antiquity for the earliest cities serves that argument. Read as propaganda it is coherent; read as a census it is nonsense, and it was never meant to be read as a census.