I am old enough that I was a big fan when this first came out. There were some of us who absolutely loved it (and that wasn't necessarily an overall cool thing in 1970 or so). And yes we listened to it a thousand times, and in a way you could hear that drumming and of course it directly contributes to the whole song. But back then, our ears were focused on the guitars. and Ozzie's great singing. I don't think we really appreciated the drums.
Now, all this time later, with Youtube and other media keeping it alive, and having evolved myself in my music appreciation, I look at it and I just can't believe my eyes. If you just listen to the song from the album with an ear for the drums, it sounds beyond amazing. Watching him actually play it in this video is just a sublime experience.
That first phase of Black Sabbath is the formation of something that expands to greatness, all because you had just the right combination of 4 guys, each of whom had amazing talent, but there is always lots of amazing talent out there. When they combined together and made up these songs, that was something greater than the sum of the parts.