"Hey Joe" is in the key of E, with some acute observations on how instrument affordances affect music structure

It seems that there has been some discussion on the internet about the key of Jimi Hendrix's (version of) "Hey Joe." Adam Neely – one of my favorite music YouTubers – explains why it's in E. He explains why conventional music theory, derived from and thus most appropriate for European classical music, just gets things confused. Starting at about 8:30 Neely talks about what makes sense for the guitar, given the way it is tuned and how it lays under the fingers: open string chords. That's REALLY important, and is the reason I'm posting this.

At 12:00 he concludes by pointing out that the tune is a blues and that the blues defies the categories of European common practice theory. For example, he talks about blue notes, which are microtonal and so doesn't exist within European tonality. In particular, he talks about the "neutral" third, which is in between a major third and a minor third (which are well defined within European common practice). This is important too.