Perhaps you could list what criteria you consider appropriate for judging the quality of a band, since innovation/influence/historical significance don't seem to impress you.
Well, innovation and influence do carry some weight, but they are certainly aren't enough to make a band THE best, since another band can always come along and improve on what you have done. For instance, Metallica were the first thrash band, but many many bands came after them, and improved upon their thrash sound, ulimately rendering Metallica as nothing more than a mediocre thrash band by the early 1990s. I'm not saying Sabbath are mediocre, since they are definitely very good (their earlier releases, at least).
Here are some things I find are important factors in how good a band is:
riff writing ability
Good riffs are sequences of notes and chords that make sense in their context, and create the music. Often, good riffs will either make you want to bang your head, pump you up or wake you up, relax you or put you in a trance, make you want to cry (depressing emotive music), or simply amaze you with their speed and complexity. A good riff is also usually more than three notes or chords or just chugging out on the E string (Hatebreed anyone?). In less than five minutes, I could teach someone who has never touched a guitar in their life to play something like Smoke on the Water or Wild Thing (these two songs fucking suck and are examples of bad riffs). Good music should be a little bit more challenging than anything along the lines of those two songs, since songs that simple don't sound good to my ears.
compositional ability
Verse chorus, verse chorus pop arangements get boring quickly. The more complex arrangements of metal and classical music are far more insteresting to me. Also, it logically is more interesting to listen to if the song has more than just two riffs.
playing ability/musicianship
Playing on tempo and playing cleanly (no sloppy picking mistakes, missed notes, or only half hit notes). It doesn't have to be super hard to play. However, playing fast and cleanly (whether in solos or riffs) is impressive, but not necessary. This is why tech death doesn't suck.
intangeables:
This somewhat ties into riff writing ability. But some bands can pump you up, serve as an outlet for anger, give you the chills, almost make you cry, and make you feel better when you are depressed. Some bands I presonally can really connect to emotionally: Primordial, Mouring Beloveth, Darkthrone, Forgotten Tomb (earlier material), Suffocation, Deathspell Omega, Burzum, etc.
I suspect that the last category plays a large role with people who feel Sabbath is the best. Though their songs personally don't move me emotionally in any way.