Not to pick a fight (just a student of spanish), but my spanish teacher would caution us against the categorization of permanent vs temporary and gave us acronyms instead because of examples like:

It is 1 => Es la una (describing time uses Ser)

I am an engineer => Soy ingeniero (describing a profession which can be seen as a temporary state of affairs)

I can't think of a counterexample for "estar", but you are absolutely right about "ser". Off the top of my head: "soy rubio" (I'm blonde), "soy joven" (I'm young), "soy ciudadano Español" (I'm a Spanish citizen).

My favorite quirk is "estoy muerto" (I'm dead), which leads to plenty of metaphysical discussions.

I still remember the mnemonic my 9th grade Spanish teacher gave for this: DONT BE LOCO DONT: Ser is for Description, Origin, Nationality, and Time. BE: these verbs mean "to be" LOCO: Estar is for Location and Condition.

Determining whether a sentence describes the subject or describes the subject's condition is the trickiest part.

Good point, I never thought about those. Still, I'd personally say these are the quirks rather than the entire premise of permanent vs temporary. This is from the perspective of a native speaker though, I don't know anything about linguistics.