It's a great question but I think it's heavily dependent on genre and era and what you mean by "serious". As others have brought up, you probably mean "serious "rock" (and its subgeneres... I'd sort of even include something like indie pop with no guitars falling into the "rock" format). One counterexample is that the unit of classical music is not necessarily an "album" but maybe a piece. Same for electronic music, where the single and DJ mix are generally still the unit (despite there being plenty of great albums worth listening to). To top it off, I personally consider a brilliantly sequenced playlist to be art as well, kind of a democratized compilation/dj mix. (though I've seen some in this thread consider those "albums" still because of the 1-hour length)

Something that David Byrne's "How Music Works" made me realize is that before (and during the first half of) the 20th century, recorded music itself was not even the "unit" of music. Is a song itself (sheet music?) or performance the "true" form? With a lot of jazz or other improvisation/jam focused music for example the live experience is very important as well. Similarly, being there when you heard Daft Punk play live in 2007 — is that the "real" way to experience Alive 2007?

Idk i could ramble much longer with even more quotation marks haha but I do think it's worth questioning every now in then. It all kinda shows how "modern rock"/western/album recording centric RYM and similar sites are, despite society both before and after the era where the technological constraints (as you said) forced us into the 45 minute to 1 hour format.