This case is more stupid (and worrying) than the Thicke/Gaye case (although, for preempting the litigations Thicke deserved what he got, despite being in the copyright clear), the Hollies/Radiohead/Lana Del Ray (just a fucking standard chord sequence), Spirit/Led Zeppelin (how can you copyright fingerpicking or chord sequences). Even the only case in recent time that had any possible grounds (Sheeran/Gaye - same tempo and chord sequence) should have been thrown out.
Just imagine Charlie Parker suing every jazz saxophonist who came after him. Or Charlie Patton suing Robert Johnson and every other blues artist that followed.
Popular music is made up of a finite number of elements; those make up its form. The ones suing could easily be sued themselves, but that doesn't try to understand the process of songwriting/production.
They say you can learn to play any song by just learning how to play a hundred songs and then you'll have all the moves you need to easily learn anything new; that's because no song is made in a vacuum. It's the reason so much music "all sounds the same".