Love the (obviously) educated analyses to support your thesis. Very well done.
I think, as well, they were a fully integrated band: All four sang lead on songs, as well as harmonized beautifully. All four contributed compositions. Their movies gave each one roughly equal screen time.
They were truly The Beatles, & not Lead Singer & the Rest as even their main rivals, The Stones, were.
When the broke up, they stayed broke up. We didn't experience their gradual decline & descent into increasingly mediocre albums & performance.
That is what makes legends.