To be clear, I am no huge Ed Sheeran fan, to be honest, (he’s OK) but almost every artist in history has been accused of plagiarism because of the limited number of notes, keys and progressions. Everyone from Led Zeppelin (Stairway to Heaven) to The Beatles (Come Together), George Harrison (My Sweet Lord), the Bee Gees (How deep is your love) and many, many more. An accusation does not make any one of these people instantly talentless. And, like the others, Sheeran has written hundreds of songs, a very limited few of which (by law of averages) have sounded like tracks by other artists. Many, many more have not.
Again, was John Lennon talentless because be 'collaborated' with Paul McCartney (and George Martin)? Or Mick because he 'collaborated' with Keith. Or Queen who 'collaborated' with each other. John Bon Jovi and Richie Sambora? Bono and Edge? Indeed, John/Mick/Freddie were nowhere near as successful writing alone as they were when they 'collaborated' with others, which only goes to show how difficult it is for ANY solo artist to be consistently awesome (not you, Kate Bush, you can sit down. And you, Prince. Michael Jackson can kneel on the chair). And that’s before I go anywhere near Holland/Dozier/Holland or anything Motown. Even the artists who get sole songwriting credit 'collaborate'. Did Michael Jackson write the guitar solo for 'Beat It'? No, that was Eddie Van Halen. Did he even write the guitar Riff? No, that was Steve Luthaker. Or the drums? No, that was Jeff Porcaro. These people were not brought in to just play what Michael told them to play - a chimp can do that. They were brought in because of what they could bring to the song. And what about Quincey Jones? Did he just sit there looking pretty or did he advise on notes, melodies, lyrics, structure, dynamics, tone and overall feel and mix..?
To say that 'actual artists write and perform their own songs' is a very uneducated statement. If you want to see 'intense collaborative process' watch 'A Year and a Half in the Life of Metallica' and look them creating their Black Album with Bob Rock and how many arguments he has with them about changing lyrics, melodies, riffs, structure, solos etc. Or look at Back in Black by AC/DC (Mutt Lange) - both these albums were full-on 'collaborations' between the band AND the producer. That’s why you bring in a good producer. It why producers get recognition for the albums they produce. Both TBA and BIB would be much, much weaker efforts without that 'corporate-produced collaboration' you seem so keen to sneer about.
