If
300 is anything, it is homoerotic not fashy. At least, not fashy on any level besides "our heroes are brave and honorable while our enemies are cowardly and devious", which is a trope that goes back to the very first story told by Ug the Caveman.
If you think 300 is a fashy movie, some support for it besides "I think it is" is probably necessary!
It is certainly nowhere near as fashy as, say,
Attack on Titan came off as, which I stopped watching because the cryptofascism and thinly veiled support for Japanese militarism was a bit too obvious.
Also, if you are going to use big words like 'diagetic', you should probably make sure you are spelling them right.
Wikitionary just calls it a misspelling of diegetic.
en.wiktionary.org
'Diagetic' is highlighted by chrome spellchecker as incorrect.
Free Dictionary when searching for it autocorrects it to diegetic.
Definition, Synonyms, Translations of Diagetic by The Free Dictionary
www.thefreedictionary.com
And another dictionary says the word doesn't exist.
Definition of diagetic in the Definitions.net dictionary. Meaning of diagetic. What does diagetic mean? Information and translations of diagetic in the most comprehensive dictionary definitions resource on the web.
www.definitions.net
I dunno, I think the 'message' of
300 is sufficiently confused that it is difficult to call it the 'ur-text' of the alt-reich on a level greater than, say, the Star Wars movies.
Like, in the movie the Spartans go "the weak can't stand in the phalanx", and send the hunchback away, who then betrays the Spartans to the Persians because he was rejected. Surely that is a
rejection of the fashy ideal about the strong needing to cut away the weak. If Leonidas hadn't been "oh you are weak so you are useless and without honor", the Persians wouldn't have been able to defeat the Spartans.
Contrast that with Star Wars. Star Wars is, off the top of my head, the only pop culture franchise where it is widely acceptable to dress up as the in-universe Nazi stand-ins for cosplay, and countless novels have been written about the Empire wasn't all that bad, the Republic and the Jedi had it coming, the galaxy needed strength to restore order, not everyone in the Empire was bad, etc.