It was more explicit about the western elements than most, but western influences are pretty common in sci-fi TV and films. Star Wars is one obvious example (irrelevantly, I thought Firefly was generally at its best when the western elements were more in the background).
Star Wars never struck me as being all that Western-influenced, though I've heard the argument made before. Except for Han Solo's gun belt (which is as much Buck Rogers as Western), I don't really see it. But then I've never tried to either.
Certainly SF space adventure has always had elements of Western themes cloaked in spaceships, but what I thought was pretty brilliant about Firefly was drawing a line under it and pushing it right to the forefront, letting them do really fun and innovative storytelling.
for its conception of a future "humans in space sans aliens",
That is different from most previous space operas (although, Red Dwarf didn't have aliens if I recall correctly), but to me that's more a matter of trappings than anything else - I don't think it made the stories work that much differently from other comparable series.
Red Dwarf, I think, is minimally SF. It's British comedy with an SF premise, but much more comedy than space opera. And a cat become human is as alien as anyone from Alpha Centauri. Non-alien futures in space are common enough in written SF, but fairly unusual in TV.
It's a bit different, but still in the tradition of characters such as Avon, Vila and Jenna Stannis and don't you think Mal, Zoe and Jayne could have given D'Argo and Aeryn a run for their money? They might not have won, but still... Besides, they certainly were involved in momentous events in the film.
I wasn't really counting the film since the question was "what was your favorite Whedon show?" And, no, I don't think Mal, Zoe and Jayne could give D'Argo and Aeryn a run for their money. I think Mal, Zoe and Jayne would have run for their money if they saw D'Argo and Aeryn coming. Jayne was strong, but stupid, Mal was smart but not really a fighter. Zoe and Aeryn might have had a throw down for two minutes or so, but then Zoe would take the better part of valor and vamoose.
As for Avon, Vila and Jenna Stanis, I must admit to being only minimally familiar with Blake's 7. The main difference to me seems to be that Blake's 7 was more of a straight heroic freedom fighter versus totalitarian oppressors - a pretty standard trope of heroic SF, whereas Firefly was more the motley crew model. If the show hadn't been prematurely cancelled I think the crew would have muddled about on their little adventures for quite some time before becoming involved in the momentous events outlined in Serenity - and those events, spread out, would have seemed a lot less momentous. As it was, no one was out to change the course of history or free anyone from oppression - they were always just trying to survive. That's a common trope in a lot of fiction, just not SF TV.
Don't get me wrong, I can see where you're coming from and I do think Firefly had enough of its own vibe to make it distinctive, but I don't think its formula was as original as Buffy's. I'd never seen a TV series before that mixed action/horror with teen/young adult drama. I think Firefly slotted in a lot more easily to an established genre.
I hear you, my friend. You're probably right that Buffy's horror/ teen angst combo was original - but I'm too familiar with superheroes to see past how much the show lifted straight from that genre with absolutely no alteration. But Whedon's at his best when he's doing that sort of post-modern genre-mixing. Like I said, Buffy missed striking a chord with me because I saw it when I was in my late 30s. If I'd seen it in high school or college it probably would have resonated a lot more. And it occured to me that the movie
Scream, which did a lot of the same things as Buffy - everyone conscious of being in a horror movie, horror/ teen angst combo, preceded Buffy by a year.