there are some great heavy single coil tones out there - the who, led zep, sabbath
Brain May anyone ??? - Sheer Heart Attack has some jaw-dropping tones on it, all from a guitar built from a fire-place, some Burns single coils, an AC30 and a treble booster. Oh, and a ton of natural talent.
But doesn't May's guitar have switching which lets him combine the coils for big humbucker-like tones? (I'm not suggesting for a moment that's what setting he used on any particular track, I have no idea!)
I agree that there are some great heavy single coil tones on record, but (IMO) mostly for lead tones. I don't think a heavily distorted single-coil matches the tight crunch of a humbucker for chords and riffs. P-90s can give a great powerchord tone, but more for that slightly woolly Doom sound.
When you think about it, a lot of single-coil-using hard rock players (Blackmore, Uli Roth, Yngwie etc) don't really use big crunchy powerchords much. It's a lot of single-note riffing.