Isn't the concise answer Philadelphia? :) Partially joking, I know this is an oversimplification.
In any case, this interview with Earl Young from The Trammps, discussing the origin of four-on-the-floor, is pure gold: https://www.youtube.com/watch?v=gsf51_a1ceI
The thing that complicates it is four on the floor has lots of predated "almost but ok, not quite exactly" versions. Such as in Brazilian pop, take Participação from 1971: https://www.youtube.com/watch?v=7DP6hRt9xvw ... those percussion aren't far away from late-70s orchestral disco. Almost same BPM.
This drum style kinda came out of everywhere. Here it is in Pakistan also in 1971 for instance, Runa Laila, Rushdi, Shaukat Ali Khan & Munir - We Don´t Care, starts around 1 minute in: https://www.youtube.com/watch?v=c9uYjpkTkNo ... that's the 73 columbia release pictured in youtube, not the original 71 odeon one.
Here you can get it in part of this 1971 Phillipines release by Dakila as well during the chorus, https://www.youtube.com/watch?v=jUKDKXSA2-8
Or what about Sophy, from Puerto Rico also in 1971: No Quiero Que Te Vayas ... a very slight change in the drums and you get disco https://www.youtube.com/watch?v=2bhdOpVs9hU ... this one-step-away stuff was common, here's Polish artist Halina Frackowiak - Do końca świata https://www.youtube.com/watch?v=lgrUUfXesdM or ピンキー グッド・バイ from 1972: https://www.youtube.com/watch?v=WeRtlpY96B0 ... ok that last one was just for fun.
Anyway, I've been trying to compile this narrative for a long time ... all the soda flavors at once smashed together. That's all I can come up with.
Can you please help me understand "rock is super messy"? The traditional narrative is "rock was mostly derived from blues (+ some other influences)" but the counter(?)example you provided is a classic 12 bar blues.
Do you have some messier examples? Or did I miss your point?
Then I gave up trying to construct it. The reality is it's a bunch of things smashed together like pressing all the buttons at the soda fountain at once. That's what happened.
That's where techno came from as well.
Sometimes the narratives are super clean, like rappers delight for rap (there's pre rappers delight style rap records, but under like a dozen or so) or the amen break and dnb or the configuration of the swing drum kit for swing music or house music proper being "the stuff knuckles plays" in Chicago.
But a few styles are inherently messy with no clean lines. Rock, Disco and Techno are three
Rock is especially super messy, here's Meade Lux Lewis in 1927 for instance, https://youtu.be/tDuLezFRMNU swap the piano with a guitar and you have 50s rock