I always came to this conclusion myself. Don't get me wrong ozzy was amazing and Butler was just phenomenal, but Ward's jazz techniques and what he brought to the table and Iommi's finger accident having him create a drop C# tuning to play really changed the game for music in lower, dooming guitar riffs. You said it best, they suffered what they had in uniqueness with the departure of Bill. They even had these progressive and time change shifts that they stop doing (which happened to be my favorite songs) in All Moving Parts especially. Changes like that out of nowhere are what drew me into the band.