Who is anyone on here to decide what grads should do with their potential, or whether they're wasting it? That's the height of arrogance, and I see no rationality whatsoever in such an attitude.
A more charitable interpretation of your parent's comment is the more general "X is a waste of your potential compared to Y, you should be doing Y." I would agree with you that startups are not automatically a better use of potential, but they might be for the particular person.
What ranks higher for me than "potential" (which is trickier for me to measure) is sanity. I can't see myself working at BigNonTechCo for 40 years doing more or less the same kind of activities, 40 hours each week. Other people can, that's for them, I'd go insane. Thus it's instrumentally rational for me to avoid such a place and rational for other people to seek it out.
What ranks higher for me than "potential" (which is trickier for me to measure) is sanity. I can't see myself working at BigNonTechCo for 40 years doing more or less the same kind of activities, 40 hours each week. Other people can, that's for them, I'd go insane. Thus it's instrumentally rational for me to avoid such a place and rational for other people to seek it out.