I think what we should be looking at is the amount of luck required to succeed. And that is most definitely increasing.
However it isn't just luck vs hard work. Hard work leads to creating more luck.
Become CEO of a unicorn? Sure.
To live a happy and meaningful life? Or give a better life to your children? Then I don't agree. I would say for most its very hard to live a a happy meaningful life without working hard. There's some chance involved, sure. It would be hard to lead such a life if you're diagnosed with a debilitating disease. But I think the primary cause of success in this sense is hard work and sacrifice.
The problem here is that "better" encompasses a wide range of things. When people say "success isn't based on hard work," what they seem to mean is that how much better is highly dependent on luck (also, without hard work and with luck you can achieve success, but not the inverse).
Relatively.
The author defines the success as the outcome for a hypothetical hard-working single mother with relation to the outcome of a hypothetical alternative where that single mother stops working.
I prefer to deal with reality, so I'd rather define success of real people as their outcomes relative to the outcomes for other real people who work equally hard.