I think it all depends, there are plenty of big companies that don't mentor, pigeon hole you into their own technology and libraries (makes it really hard to break away from unless you plan to stay there your whole life). Some startups do well, but they don't have the financial backing and when a big project gets cancelled they collapse (been there, done that). I worked for a startup part-time while attending college, it was one of the best things I did, I was the 7th employee and when i left to finish up college they were close to 20... by the next summer the company was done. Turnover now is high everywhere, I have yet to find a place where a person has worked there more than 2 - 3 years, and to be honest in 2 years you won't learn much depth (software is code + language + stack + domain knowledge + customer knowledge). I think the article is more about someone who moved too quickly between bad jobs, and fell on the data scientist path (which is not bad, just sometimes you do have to fail a bunch to find something good).