The next level above financial independence is financial freedom (you can just get whatever you want, from shoes to houses) - off the top of my head I would guess this is probably around the 0.01%, which would be about 32k people in the USA. As an example of freedom, these people can buy nationality and avoid immigration limitations (going rate is ~$1-5m).
The article is way off just comparing salaries. There are 3 social classes in terms of having a meaningful lifestyle distinction - those who have to work for someone else, those who don't, and those who have full freedom to decide where they go and what they do each day. All they did was compare a bunch of people in the same social class (somewhat shockingly the Romans considered this equivalent to a slave class).
J suspect that ceteris paribus, being frugal reduces happiness - by definition, it's not getting things you want to get.
Once you can afford something that was way out of reach before, you buy it and after the first few moments you realize it is not as great as you expected. Do this a few times, and you'll learn what is important. The more wealthy people I know do have a slightly above average car and house, but IME the biggest difference is that they have far more extreme - both in amount and in price - experiences, i.e. weekend trips, fine wining and dining etc.
Higher earners tend to just upgrade and spend more (apartment, clothes, restaurants, hotels etc), and aren't really living that differently - that lifestyle can certainly soak up maximum income achievable in a salaried job.
I think this is what the article inadvertently pointed to, that the higher salaries could lead to a sense of frustration that nothing really changed.
If you no longer have to work, and you choose not to work because your current job isn't ideal, it can be hard to get the motivation to search for a new job. At the same time, without work, it can be hard to find purpose.
So you might be stuck in a situation where you aren't working and struggling to find meaning.
There are plenty of financial reasons, but isn't that what we're talking about? If you have enough money that you don't have to work for the rest of your life, you probably have enough money that you can spend your time on whatever act of creation you find fulfilling.
Purpose without existential risk of failure is not usually perceived as genuine.
If you have enough money and only put a fraction of it to use, you might create things, but you're never really risking anything. I'd wager more people join the military for purpose than the local paintball team, not despite but because the former really puts your life at risk.
Says who? That may be associated with lutheran ethics of hard work, but doesn't look like an universal nor an essential requirement. Was Mother Theresa devoid of purpose because there's no way she could fail at taking care of people?
That's just as common in many other non-Western cultures, such as Japan, South Korea, China. All three are materialistic and work-centric. Japan has extreme work identity, South Korea is barely a notch lower than Japan on that. Both put the US - and the entire West - to shame on work-centric life (for better or worse depending on your views on such things). China today is one of the greatest materialistic work cultures that has ever existed. You see it in all of China's markets and businesses today, and the move from rural to urban to seek greater materialism and elevated work identity. It's an intense fever there, eg:
https://www.theguardian.com/world/2017/apr/04/china-plans-bu...
One of them was the president of an insurance company and he was ousted in a Machiavellian political maneuver, because he fully expected to hold that position until his health failed him or he died at the post.
You can see it in the current crop of 80-year old politicians in my country. One of them wants to go up for re-election and he would be in power until he was 90 years old...
If you have financial independence, you have the choice to work or not, and if you do work, to do whatever work you find most meaningful.
Without financial independence, you have no choice but to work, and for the vast majority of people without financial independence there isn't much choice of what kind of work to do either.
Volunteering and creative experimentation fills that gap just fine.
That's certainly the line that society wants people to believe. A lot of people want a job that gives them a sense of purpose, but I'd be surprised if as much as 2% of the workforce think their job gives them a sense of purpose right now. I think we're just lucky that the majority of people don't question whether or not their job is ultimately necessary, and choose not to bother when they realise it's a waste of time.