"But is it right that Sheeran should cash in without sharing the profits with an artist he's so clearly inspired by?"

Yes! For one thing, that's what everyone does. For another, it's how music evolves. For a third, it's what gives you a wealth of choice as a music consumer, and how we can discover and enjoy hundreds of similar records in styles that we like, be it late-70s disco, synthwave or late romanticism. Indeed, for a fourth, it's how genres and styles are born and sustained! #DoneForNow