This is a pretty odd claim. The sentence is grammatically coherent and the semantics are... there. They're hard to understand, but that's true of essentially all ancient writing; this problem becomes obvious when we try to date historical events by reference to astronomical phenomena that contemporary texts mention. It's easy for us to calculate the precise dates of interesting astronomical phenomena more than a thousand years in the past... but it's difficult to determine exactly what the texts of that period mean when they describe astronomical anomalies.

(For something similar and much more recent, here's part of the introduction to The Troubled Empire: China in the Yuan and Ming Dynasties:

dragons were spotted seven times in the seventeen years from 1351 through 1367. In that final year, the Yuan dynasty's last, there were two spottings. The first, on July 9, was in Beijing. A dragon emerged in a flash of light from a well in the palace of the former crown prince and flew off.

What happened there?)

Why is "Diphilimus is cityless" more meaningless than a standard Linear B inscription such as "small jar, no handles: 1 handleless jar"? By most accounts there is more meaning in the sentence about Diphilimus.

> Greek (both in Linear B and later) doesn’t use the -us ending like Latin does, so its use here in a “Greek” sentence is very suspicious.

Reasonable. But there are many Greek names that do end in -eus, such as Theseus, Perseus, Odysses, Achilles, and Zeus; the reader cited above specifically suggests that the Ventrisian sequence ai-ke-u might be interpreted as the personal name Aἰγεύς. Diphilimos does not appear to be a classical Greek name, so we don't seem to be committed to any particular such form.

Lacking syllable-final -n and -s, how would we represent the name of Tiryns in Linear B?