But there are some – e.g. Auszeit. And at the same time, we use ß in locations where it'd otherwise be ss. While it started as a ligature, its current usage doesn't fit that.

That doesn't mean it's not a ligature. If English still had a "th" ligature, the word "outhouse" wouldn't use it.

Interesting claim ... a similar compound word with a present-day ligature is "halfling." TextEdit renders that with an "fl" ligature, but should it not?

Is w then still a ligature of vv, and should vve remove it?

th in English wouldn't be a ligature, it would be a letter (thorn or eth).

Absolutely true, it's not really its own letter nor is it really a ligature. It's an unique feature of the german language, which is hopefully here to stay...

It's more apparent if you look at the long s (ſ) which has since fallen out of favour.

If you squint and your font permitting, ſz should look more like ß.

Or, even more similar, ſƷ. (Which is long s (ſ) + capital ezh (Ʒ))

There are tons according to http://www.wordmine.info/Search.aspx?slang=de&stype=words-wi...

FRAKTIONSZWANG FREIHANDELSZONE KONFISZIEREN [...]

A lot of them are combined, but still quite a few 'regular' ones

Here is the full list of non compounded words containing an "sz".

Abszeß - Adoleszenz - Disziplin - Eszett - Faszie - Faszination - Fluoreszenz - Koaleszenz - Konfiszierung - lasziv - Lumineszenz - Obszönität - omniszient - Oszillation - phosphoresziere - Plebiszit - Proszenium - Rekognoszierung - Rekonvaleszent - Szene - viszeral

Most of these actually are of latin origin. My favorite is obviously "Abszeß" - probably the only word in the german language that will show a non compounded co-existence of "sz" and "ß".

It did, 20 years ago ;)

Nowadays it's written Abszess as the e is short.

FWIW, in all of them the "sz" spans a syllable boundary (yes, even "Szene" although I despise the syllabic "S" with a vengeance because it's so awkward).

Yes, historically it's a ligature.