"it is a graceful, elegant - even minimalist - design."
Look on the bright side, I can agree with the overall sentiment of your post, I could just express it in a more minimalist fashion. Omitting a couple of words!
While we're still off-topic, though, it pays to be careful quoting Cocteau (who I was a fan of as a teen and through my twenties, and still have a half-shelf of books on his work and life). He said a lot merely for effect, and personally I'd pay more attention to contemporaries such as Erik Satie and Piet Mondrian who had far more to say about simplicity - informed in Mondrian's case by Hegelian philosophy. Like his far more influential contemporary, Marcel Duchamp, Cocteau was an outsider struggling for acceptance, especially by wealthy patrons(!), partly because like Duchamp he wasn't a top-tier artist (making the Academie late in life, for film). They both made their impressions by being outrageous, more style than substance. Duchamp's rebellion led to Art being somewhat redefined, Cocteau didn't manage anything equivalent to that, and his major personal accomplishments were usually collaborations. Even then he had a hard time selling himself to people like Serge Diaghilev. He became very aware that appearances were more important than substance (at least to him), and that sense informed almost everything he said, even about the topic of "less is more". If you're going to quote a master of ambiguity like Cocteau, how about "I am the lie that tells the truth" - that appearances are deceptive!
Which I guess brings us back to the A350, it looks minimalist (if you must) but that's not what it is. If the design stops at the skin then it's simple enough, but no more than other designs out there, as a whole, though, it's an example of one of the most complex machines humans make. Minimalism isn't in its DNA.
So if we are in fact talking about superficial aesthetics (we must be for the term minimalist even to make sense), what about the A350 looks less complicated than the 788, and the answer surely is "not a whole lot". In fact, to me it seems that the 787 is less fussy, not by much, but apart from engine chevrons, it is more "whole" - of a piece.
When, as a kid, I saw the prototype A300 at Hanover way back in 1974 I couldn't help thinking that such a plain design was probably the future and not especially appealing. Fast-forward to now, and the designs are fundamentally the same, the only recent revolution (appearance-wise) being in aerodynamic treatment of the cockpit area thanks to advances such as computer modelling and fabrication. Flap tracks & fairings, engines, gear etc have not fundamentally evolved in the same way. I'm sure flap tracks could be faired in more subtly and look far more "minimalist" if the trailing edge structures were faired in differently, but I assume there are aerodynamic advantages to keeping them looking like breakwaters, in this case directing airflow directly across the wing rather than allowing lateral flow.
There's a case for calling almost all aircraft shapes "minimalist" if that's the case. I don't think the A350 stands out in that regard. To me, the A350 fuselage is certainly nicer-looking than the 787's - it's something that Airbus seems to get right all the time and Boeing, not so much. The 787 starts well but the rear fuselage just doesn't gel, but in all other respects I actually now prefer the 787 to the A350. The wing is infinitely more graceful than that of the A350 to my eyes, particularly the trailing edge. Does the fact that Airbus deleted a fairing at the base of the tailfin make the design minimalist, or does making the tail look like a second object attached to the first like a snap-together kit actually complicate the design - remove its sense of whole-ness? Even SOCATA's attempt to delete the tail fillet was eventually reversed, and I'll be interested to see whether Airbus relents and adds that back in a few years down the line.
I think Caltech makes a good point that we need to be mindful of partisanship getting in the way of objectivity. There's no taking away from Airbus their vast achievement of making market entry back in an age mired in incumbent aircraft manufacturers, the investment and belief is genuinely staggering and admirable, and the designs eventually got the chance to sell themselves because they're perfectly good designs.
I dislike the 777 for my passenger experiences in the plane (BA), it's noisy and wearying to fly in, I like the A330/340 for noise reeasons and also for the "floaty" nature of its flight that I put down to being the wings and how they deal with turbulence. I also prefer them aesthetically, but that doesn't make the 777 a bad bet, and certainly doesn't justify carping about issues that crop up. These vastly complex machines live a helluva life, and things happen. The last major dropped ball was Boeing's battery issues with the 787 that came up in testing and yet entered service (shades of the DC-10 door issues) because Boeing was on the back foot time-wise and made bad decisions. That doesn't mean I (or anyone) should be carping about it now that it is proving itself in line service. What's past is past - we can only go on flagellating Boeing if they've done nothing about it. Same for Airbus.
Okay, back to lurking, I guess.