What kind of argument is that? It's backed by absolutely nothing. It also conflicts with everyone I've ever known.
Also, from the discussion here, the OP's definition of rich is a dubious one: "But generally, I think if you have a couple hundred grand in the bank you're rich."
If you're an employee, and assuming you've already paid taxes on that 200k, and you don't have kids in school or health problems, that's going to get you a few years down the road. It should be enough runway to get a new job with room to spare. As emergency money it's pretty good.
If you're working with 200k in the bank what does that get you? A down payment on a house you can't really afford? Maybe a sports car? Again this is assuming you're not going to put kids through school. That 200k means you're rich if you don't spend it on anything rich.
That 200k is decidedly not an amount you're going to retire on. You could take that 200k and start a business, but then we're in conflict with the idea that starting a business is completely unnecessary for obtaining riches.
Having said that, I'd be very curious to know how many startup jobs made an employee 200k richer after they've moved on. Given that many startup jobs (at least in the US) are in the Bay Area with its high rent and high taxes and that the average startup salary is what, 100k? IIRC, 100k is going to put you at close to a 40% tax bracket in SF. So that's 60k - 24k for rent for the year? That's not a lot left for a lifestyle in that area. Assuming you saved very aggressively you could, at the outside, put 20k away a year? So that's 10 years. What could you have accomplished working for yourself over those 10 (critical) years? Possibly less, though I think the numbers are probably in favor of a 10-year entrepreneur in a field with low barriers to entry.
What percentage of the current crop of startups will ever see employees make significant amounts via their stock? If you want to roll the dice that way certainly the numbers favor the entrepreneur.
Work for someone because you believe in what they're doing or you simply need the money. Don't ever do it to get rich.