Well, in my view, the author might have unfairly characterized all arts as having too much in common with each other. I know nothing about filming. Before I became a professional writer (for a company, not actually writing books), I was an aspiring musician and, let me tell you, what he says is very accurate for this 'career'.
All the bands (or 'projects' as we liked to call them) I've ever been in (more than 10 in the last 15 or so years) thought we could have made it; 'making it' meaning having monetary success or 'living off of music'. All of us failed except one of my ex-band members.
The problem is, as the author suggests, it's not really about skill, though there is a level of skill needed to be successful. That level is very low, though, whereas in other professions that skill level might mean a 30, 40 or 50k salary difference.
As a child, I thought playing music was about skill, so I learned classical guitar, and, according to my friends, I was the 'best guitar player they knew'. I always got compliments at shows and on my own albums. I was never even close to being found out by an A&R guy or signed to a record label. And guess what? There are a lot of people like me. 10 years ago I got really into jazz and that was my new circle or 'thing'. I came at music more from a jazz perspective because I knew theory and deconstructed tunes (in all styles) whereas rock musicians don't really like to do that and many of them can't. I remember going to the jazz festival and talking to musicians telling me how 'Yah, we're signed, but we don't even get a free copy of our album. We have to pay for it like everybody else'. These local musicians are successful because they live off their music, but many of them have modest earnings that pay the bills. They can't afford vacationing every year to somewhere fancy and most have beat-up cars, maybe a wife, and no more than one child, if that. They are very humble people.
(And yet, and yet) you have people that can hardly sing a note that are famous where their work is based on great post-production sound engineers. It's easy to be bitter about the music industry, but a lot of them aren't. I know I'm not and I listen to Justin Bieber without a problem (though my friends and family think it is very bizarre of me to).
The way you reach monetary/economic success as a musician is usually about non-music-related stuff you do, which is strange because in most professions, the way you become successful is by practicing your art and honing your skills.
My only friend (my ex-band mate) that is 'successful' tours the world and lives off music, but he barely breaks even, since they have to pay for studio costs, equipment costs, accommodation, car/transportation costs, roadies, etc. He loves it, but he says it is extremely difficult and gets depressed easily. This particular friend knows his limited skills so he goes more for showmanship and energy and getting people pumped - he plays garage rock. The funny (interesting) thing is his band was about to disband when all of a sudden the right A&R guy discovered them. It took probably 4 years of touring the country (Canada) and some parts of the States all on their own expense while having full-time jobs and doing it on their vacation time. Thousands of dollars. He was doing it while we were in a band together and with our band we burnt over 10k of our own money in only a year and a half.
Now when I hear him on the radio I love it. I'm so proud of him (and I can picture everyone laughing at me for being such a nerd). But there is a huge element of luck and he knows it. You work hard and don't expect to make it, yet you put yourself through it because you love your art, your music. And you do this for decades.