It's also telling that a guitarist can be replaced by a synth
You still have to have someone to, you know, play the synth. You don't need anyone to play the drum machine.
Also, if we're talking about contributions to the band, need I point out that Heaven & Hell (aka Sabbath without Ozzy) was fucking awesome, and Ozzy solo is wimp bullshit?
Leaving aside the dubious notion that Heaven & Hell was "fucking awesome" (a statement that makes sense only if you're using "fucking awesome" to mean "boring, trite, and phoned in for cash"), not to mention the fact that the H & H drummer was, in fact, the very same Vinny Appice you have consistently maligned elsewhere (incidentally, he was behind the kit for the best of the original Dio-era albums,
Mob Rules), the point you've made has no relevance at all to the issue at hand. We're talking about the contributions of various members to the success of the original incarnation of Black Sabbath. Dio-era Sabbath and H & H have fuck all to do with that question.
Finally, and I'm tired of saying this, but the drummer makes as much difference as the rest of the band.
No, he doesn't. Remove the guitars or the vocals, and you fundamentally alter the meaning (and even the genre) of the work. Remove the drums and all you've done is...remove the drums.
Black Sabbath was a group effort.
Creatively, Black Sabbath wasn't a group effort: it was solely the work of Tony Iommi and Geezer Butler, who wrote all of the songs. Ozzy's unique vocal sound and his abilities both as a frontman and a master of hype production were instrumental in the band's commercial success. Remove any of those three guys from the original Sabbath lineup and the whole project is DOA. Remove Bill Ward and, at worst, you get a band that is marginally less successful, but probably doesn't miss a beat at all. His contributions just weren't as significant as the contributions made by the other members, so why should he be treated as co-equal with those who brought more to the table (and, frankly, STILL bring more to the table)?