There is another facet to your second point, I think. Even if the upside from the "sure thing" two years before they IPO is not great from a financial perspective, the career growth is much faster than joining a mature mega-corp. For example, many people who joined Google/FB/Twitter a year or two before the IPO are very senior at those companies now. Granted, not everyone who joined Google in 2004 is a VP, but the probability of rapidly growing your career as the company grows is much higher than for someone joining Microsoft in 2004.
That fast career growth leads to either 1) High compensation ten years later as a director/VP or 2) Exec roles at sure-thing unicorns with meaningful equity, should they choose to leave Google/FB/Twitter.
I think there are two justifications to go early stage if you care about the financial aspects:
1) Be the founder, as you said
OR
2) You have concrete reasons to believe that the company has a meaningful competitive advantage in a large market.
These examples are far and few. For example, Google in 1998 had a meaningful competitive advantage, but Facebook in 2004 certainly did not. WhatsApp in 2010 did not, but I'd argue with Carmack, Oculus might have had (although unsure in this case). As you said, it's really hard to say at such an early stage.
Of course, if financial upside is not a major concern, then impact, agility, working on interesting stuff, avoiding mega-corp red tape, are all valid reasons to go early stage.
There is another facet to your second point, I think. Even if the upside from the "sure thing" two years before they IPO is not great from a financial perspective, the career growth is much faster than joining a mature mega-corp. For example, many people who joined Google/FB/Twitter a year or two before the IPO are very senior at those companies now. Granted, not everyone who joined Google in 2004 is a VP, but the probability of rapidly growing your career as the company grows is much higher than for someone joining Microsoft in 2004.
That fast career growth leads to either 1) High compensation ten years later as a director/VP or 2) Exec roles at sure-thing unicorns with meaningful equity, should they choose to leave Google/FB/Twitter.
I think there are two justifications to go early stage if you care about the financial aspects:
1) Be the founder, as you said
OR
2) You have concrete reasons to believe that the company has a meaningful competitive advantage in a large market.
These examples are far and few. For example, Google in 1998 had a meaningful competitive advantage, but Facebook in 2004 certainly did not. WhatsApp in 2010 did not, but I'd argue with Carmack, Oculus might have had (although unsure in this case). As you said, it's really hard to say at such an early stage.
Of course, if financial upside is not a major concern, then impact, agility, working on interesting stuff, avoiding mega-corp red tape, are all valid reasons to go early stage.