I agree with your basic premise here, but I'd hesitate to include QT in this company. He hasn't exactly "invented cubism", cinematically speaking. I'd be more tolerant of his shortcomings if that was the case.
I'm not so much putting Tarantino on their level, as much as just showing the value of indulgence in cinema. Or any artform. Even if QT is one or two or a hundred steps behind the true visionaries, doesn't mean he shouldn't be indulging himself. It's how an artist gets their DNA into their work. Yes, in the case of Tarantino, you get bits and pieces that sort of flub it. But who cares, if the instincts he trusts give us the scenes that work so well. And I'm also not one much for 'well, couldn't he have just cut the bad stuff and left in the good stuff'. The old White Album argument. It treats the idea of a perfect product blotting out the value of an imperfect one (when they really can have equal values in a lot of ways). Sometimes its the follies which endear us. Or give us a window into the artists thinking or obsessions.
Basically I don't get, nor do I want to get, how 'indulgent' has become a short form criticism for having one's time wasted. For me, its much more likely those films which stay on this side of good taste and try and give an audience a little machine that works perfectly instead of instinctively, that are the waste of time. Because its in (most cases) through instinct where we find the real emotion. The kind of emotion that isn't manipulative or contrived and designed to have us react in very specific ways. And while on the surface of a Tarantino movie, much of his action may fairly be described as artificial and manipulative, the heart of his films lays elsewhere. It can be found in these love letters he makes to the kinds of films he loves. The kind of actors he wants to cast. The dumb QT beat poetry he wants them to speak. And its in those indulgent intentions where his movies mostly speak to me.
Also, when they are banging, they are entertaining as ****.