There are many 'formulaic' genres; I guess that's what 'genre' is: a formula. There are ways of being experimental and , ahem, pushing the envelope and Led Zeppelin did this with some vim and vigour. Blues is no more formulaic than any other genre really; reggae, different jazzz idioms, rock and roll all have their touchstones and modus operandi. I think, as you say, being a young hippy at the time we were subjected to the 'blues boom' of the late 60's'early 70's; a whole bunch of not always very competent British bands giving the Americans a taste of their own bluesy medicine. It did get very boring, I agree, but it did allow the discovery of the great blues artists like Robert Johnson, Muddy Waters, Howlin' Wolf etc and my favourites, 'Lightnin' Hopkins, John Lee Hooker and Son House. All these geezers do something unique with the formula, be it guitar styles, the voice or in Robert Johnson's case everything! It was a very subtle art form in the hands of these guys; less so in the hands of British imitators with their loud electric guitars and caterwauling vocals! Oh I don't know...I liked a lot of those bands because that's what we were given as alternative/underground/progressive music and it suited our long hair and teenage rebel posturing: some I still like today and I play their records although I see their limitations now. It's just music, Freddy, after all and God knows there are more important challenges facing our planet today.
All the best.