Let's say you have a band that you absolutely adore listening to. You love listening to the studio version of just about anything they put out. More importantly, by some chance you've never heard them live (fairly common in today's world of digital distribution)--until now. Somehow, this band that you love, for the lack of a better word, sucks when it comes to live performance. Maybe their voices are a bit shaky, or off key--whatever it is, it sounds nothing like their studio recordings. What's the right response here? Ditch the band and find one that can perform live well?
In short, it depends. Obviously, I'm not going to tell you what art you should and should not consume, all I can try to do is convince you that for an artist a good live performance should not be the litmus test for excellency. Instead, we should look at the relationship between you and the artist's music, and the relationship between the artist and his own music.
Starting with the former, we should ask ourselves: is it the physical act of performing music that enchants us, or the music being performed itself? My conjecture is that it's more likely to be the music being performed itself. Think of a player piano for a moment--one of those old upright pianos that can play music without a human player. Even though it will flawlessly play Beethoven or any other piece of sheet music fed into it, no one would ever call a player piano an artist. The reason for this is because the piano had no part in the actual creation of that music; it simply reads and plays perforated sheets of music using a clever internal mechanism (as an interesting aside: these perforated music sheets are likely the first examples of structured programming languages). In other words, it's not the technical rendition of a piece of art that makes it beautiful, but the original thought that conceived it to begin with. At best, all an artist can hope to accomplish in their career is to transmit some small part of the awe that he feels in his brain to your brain. And if the artist accomplishes this with a studio version, then mission accomplished, and any live performance thereafter is superfluous.
Please note, however, that I'm not denying that there is artistry involved in playing a musical instrument (including the human voice); there absolutely is. And appreciating musical talent and artistry in that respect is a wholly separate topic that I'm not at present discussing. What I am arguing is that we (your average music consumer) don't listen to Jimi Hendrix for his mastery of the guitar, we listen to Jimi Hendrix for the string of sounds that his mind was capable of producing (though his mastery of the guitar certainly aided in this step, but that's neither here nor there). If a machine played a Hendrix song without error, and sounded identical to his version, we wouldn't truly care which version we listened to. It's the original thought and emotion that created the music and the emotions and thoughts that the music creates within us that we appreciate.
To reiterate the point one more time, let's look at one example of art from a different medium. Consider Salvador Dali's The Persistence of Memory:
While Dali's technical skill is impressive and should be appreciated on it's own merit, the painting per se should be appreciated for an entirely different set of reasons. As some examples: the painting's representation of a salient aspect of the human condition (the passage of time and our mortality), and the way in which Dali uses aesthetics to project that representation (surrealism).
Would you appreciate the painting any less if Dali were incapable of replicating it exactly, or even remotely close? Probably not. What matters is that Dali had this beautiful thought in his head, and by chance had the skill necessary to put it to paper. Even if Dali were a terrible painter, but had a vivid enough imagination to picture this image in his mind's eye, and the communication skills necessary to dictate what he sees to an artist capable of rendering it, then the painting would still be impressive with respect to Dali. Of course if Dali's dictation in this hypothetical scenario of what he sees in his mind was less than perfect, and left some ambiguity for the other artist to interpret, than the other artist would certainly share the credit for his contribution. Otherwise, it would be no different than creating a picture on a computer and printing it out without attributing any artistry to the printer itself.
Moving back to music now, based on this principal, it's also important that we consider the artist's relation to his own music. If, for example, the artist had little or no hand in the creation of his music, then for all intents and purposes he's worse than the player piano. At least the player piano can perform at a live concert and sound good. For this reason, pop "artists" who neither write their own music, nor perform it well, should at least be considered lesser artists with respect to those who do either of those things. And those pop artists who neither write nor perform but generate volumes of income for corporate labels... well that's an entirely different circle of hell, I mean future blog post idea.
What it boils down to is this: Did the artist have a beautiful, awe-inspired, or awe-inspiring thought? Did he deliver some morsel of that thought to your mind? Did that morsel, upon delivery, resonate within you and cause some sort of emotional response? If the answer is yes to all of these, then the artist succeeded where most fail miserably, and should be commended thoroughly. What makes art "art" is not how well you can replicate it, but the emotional impetus (whether it's some social critique, a personal experience, something entirely abstract, or anything in between) and its aesthetic encapsulation that makes it "art".