Re: Ed Sheeran
You'll get sequences that are similar (Let it Be and No Woman No Cry for example) and that's because the sequences sound right and therefore will have to be used at some stage more than once - any doowop song and many pop songs of the fifties and early sixties had pretty well the same structure (Diana/Why Do Fools Fall In Love/Oh Carol/Will You Still Love Me Tomorrow/Return To Sender/Girl Of my Best Friend/Maybe Baby and a million others, with variations)
Can't be helped, because they're such strong chord sequences that are technically 'right' together, but then you get the out-and-out copies, a famous one being My Sweet Lord by George Harrison, being deemed a rip-off of He's So Fine, by the Chiffons.