Hendrix has been dead for twice the length that copyright originally lasted, and for longer than the copyright period at the time he was alive (i.e. during his life when he was assessing the economic fairness of creating his music, he would've expected his work to already be public domain today). My daughter is older than her grandmother was when that music was written. Why would we care any more than e.g. what Francis Scott Key wanted?

A decent proxy for the maximum appropriate length of copyright might be when the next generation starts making those edits or disclaimers for changing culture (so the original is no longer considered appropriate for current markets), so at most ~20 years or so. One generation, and then it is history/heritage to pass on (or critique, as the case may be).

Who made his guitar? It seems like he made all his art on the back of someone else’s work… they should be getting royalties for every track made with their product

(I’m pointing out the absurdity of trying to assign ownership within a system of shared creation)

Too bad because she isn't either way. It's all going to shareholders and top executives.