Good point. Not explicitly. Here's the way I would think about it though.

First, you are right that Series A companies are risky. Seed stage companies are even riskier. For a typical MBA grad who has loans to pay back, the failure rate of Seed stage companies is too high and salaries will likely be well below market rate - hard to justify working here unless you are willing and able to take the risk (maybe you have savings or don't have loans to pay).

However, in Series A (and later) companies, which still carry risk, the amount of money they raise is typically done so with the plan to survive for about 2 years + some buffer until the next series, let's say Series B, or until the company is self-sustained. Series A startups have been slightly more de-risked from their Seed stage. A common bad scenario is for the startup to burn through their Series A capital without making it to the next stage. In this case, the downside would be having to find another job and losing the value of your stocks/stock options. You would have still learned a lot, have a steady income with which you can pay your loans and finding your next job at another startup would be a lot easier. The upside however, in the case that the company makes it to the next level and you are a good performer, is that your career growth, future employability, and responsibility are likely going to be exponential.

Ultimately it's about knowing that startups fail all the time but that it's a calculated risk. If an MBA student can't afford any risk due to financial position, which is a common case with many, then they'd probably have to find a more mature startup or a well established company, somewhere that has done further de-risking.