I think Uncle Bob's idea comes from the (misguided) idea that the software industry is comprised of folks who live and breathe code, love solving complex problems, and want to be the best of the best. For a lot of people, this might be the case. Maybe it used to be like this in the early days of tech. The problem is - for many, perhaps even most developers, software development is a job. It's not their passion (maybe it used to be!), they don't want to study and prep after hours, they just want their paycheck. A paycheck to support themselves, their family, their lifestyle, whatever it may be.
It can breed a toxic work culture to believe that yourself and your coworkers should be studying and advancing their skills outside of work. This isn't required for other professions. Yes I read the bit on doctors and lawyers, but are software developers comparable? Is it not a bit presumptuous to compare our work to those who studied for a minimum of about 10 years in universities, go through licensing exams, etc when our work doesn't even require a university degree? There's no 6 month bootcamp to be a doctor or lawyer. They're legally required to keep up to date on their skills because the requirements to enter the job are so high to begin with.
The fact that a company values your output casts a hierarchy ordering individuals by the quality, quantity and character of their output. All else being equal, people who put in more time to learn will be more effective (and therefore valuable) than those who don't. It's not a "toxic" fact, it's just a fact.
Bob's advice is merely an estimate for what it takes to gain upward momentum in the hierarchy. It seems from your argument (correct me if I'm wrong) that you find Bob's ideas "misguided" because your analysis is rooted in the notion that the number of people actively trying to climb the hierarchy somehow diminishes its existence. The hierarchy exists whether you participate actively or not---because it's induced by the free market.
And sure, there's no 6-month bootcamp to become a doctor. But there are no doctors working on non-critical projects. If you were hiring a team to craft software for a life-critical medical device, you wouldn't hire someone out of a 6-month programming bootcamp either.
There's certainly evidence in the psychometric literature showing conscientiousness is a strong predictor of professional success. The explanation for that is precisely the one I give above. You can therefore argue that the number of hours in Bob's estimate of how much time should be spent learning is too high, but you can't argue that it's misguided.
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