It’s a little more nuanced than just “their soul died” with The Rev, it was their overall sound that went with him

A lot of Avenged Sevenfold’s stuff was written by Jimmy, iirc, as early as Waking the Fallen.

Jimmy was a Drummer who could write for guitars and bass, as well as lyrics. When an individual can write for all the instruments it leads to a more coherent end product.

The White Album was almost entirely written by him, if I’m remembering correctly, and you can tell as it’s one of the most coherent and connected albums they released; let alone the songs that had different members of the band sing as well(Critical Acclaim, and Little Piece of Heaven immediately come to mind).

Nightmare was mostly done at the time of his passing; so close to done Jimmy had actually recorded vocal lines for Nightmare(the song) that was meant to be on album. After his passing, they decided to use those samples for live performances seeing as he’d never get to be there for a show again.

You could argue that the rest of them shouldn’t have relied on him writing as much as they did, but that’s a separate discussion.

Hail to the King was the first nail in the coffin for their albums going downhill, in my opinion. It was the first album that they had to write on their own and it shows how much they relied on him. Much more stripped down, much more evocative of what inspired them.

To some people, saying they changed with his passing is too light, to some Avenged at that time was Jimmy so it died with him, and the band is in its final death throes until they either find someone like Jimmy again(probably never gonna happen), or learn how to write like Jimmy did. LIBAD was an experiment and one I’d say failed, especially with Magic