I have no doubt that production is a talent and a skill, and thus, I do not doubt its impact and value.

You say this, but you don't really believe it. Nobody does. People pay lip service to it when they realize that that they've denigrated the skills of another person without really understanding how or why. Here, check this out:

I would think Brian Eno serves as a good exception. I have my doubts that Music for Airports would be what it is in the hands of another producer.

Here are three parallel points:

"I would think The Beatles serve as a good exception. I have my doubts that Sgt. Pepper would be what it is with George Best playing drums."

"I would think Guns and Roses serve as a good exception. I have my doubts that Appetite for Destruction would be what it is with Tracii Guns on guitar."

"I would think Metallica serve as a good exception. I have my doubts that And Justice For All would be what it is with Cliff Burton on bass."

These are nonsense statements. People don't make them. They are self evident - change the lineup, change the music. The influence of a musician on the music is without question, despite the fact that session mercenaries are used all the time. Yet questioning production choices is de rigeur unless the producer is huge and the talent is tiny (Phil Spector, Dr. Dre).

You're a bit of a rivethead. You've probably heard some Skinny Puppy. Most all of it was produced by Dave Ogilvie. Then he made the mistake of referring to himself as an "unofficial member" of the band and the other three got pissed and ran off and made The Process. It killed one of 'em and created the most expensive, least-selling, worst piece of shit in the discography of band. Meanwhile, Dave Ogilvie went off and mixed some Marilyn Manson, some Killing Joke, some Queensryche, some David Bowie, you know, little indie hopefuls. Skinny Puppy is back playing clubs to pay the bills and Dave Ogilvie is mixing Carly Rae Jepsen.

Here's a direct parallel to your question:

Do you think it is more common than not that the artist will fall short of what would have been done given the production being placed in the hands of another?

"Do you think multi-instrumentalists give better performances if they allow other musicians to play with them?"

I can play keys semi-okay. I can play two, maybe three chords on guitar. I can keep time on drums. I've never even attempted bass. I can totally sit down and compose a song with keys, guitar, drums and bass. I'm well aware that any music I attempt will be vastly improved by involving others on guitar, drums and bass because they are neither my passion nor my expertise. And, frankly, unless the people I bring aboard are substantially worse than me, I'm better off having them around even if they're just as mediocre... because at least they can focus on the task at hand.

Music for Airports is the album it is because it was intended as a deliberate exploration of the process of music as opposed to the composition of music. Brian Eno was focusing almost entirely on the effect of sound in a tense environment, not on making an album. He's much more focused on engineering than musicianship. As such, it sounds nothing like Roxy Music. You might as well ask what Flying in a Blue Dream would sound like without Joe Satriani.