I was working at a small startup circa 2015, around 100 employees. We looked carefully into payment providers to try to reduce costs. Turns out Stripe was very small, we would be their main customer with a 2 digit percentage of all transactions if we moved our payments through them.
Stripe had (has?) few customers and little volume. Meaning very little revenues, because that's a small percentage fee of all that. It was a fairly risky business and it wouldn't be sustainable without a fair amount of capital upfront and many years.
Lyft and Slack were much much smaller back then, also private companies that don't publish any numbers. Not exactly great references at the time.
If you have to learn something from this, it's that Stripe is a long term play, that really needed the capital to sustain and grow the business. The main growth factor by the way is the second-order effect of growing with their customers, and they're very smart to advertise to the HN crowd.
If they are not pushing everyone to work late hours and long weekends ... then there's little reason to expect that later employees should 'get rich' from a buyout - though they should get something.
Earlier / Senior staff should get something more as well.
Worth noting: Canadian 'News Magnate' Conrad Black went to jail for 'carving out' sales of assets like this as kind of a sales fee. The shareholders not only sued him but he went to jail over it. The tiny but important difference would be the 'buyout carveouts' are backed by shareholders to incent execs to stay on while Black's dealings were ostensibly not (although they probably should have been). And of course Black was a foreigner and this has a material difference in the USA (and many other countries) where non-citizens end up getting treated differently for a variety of reasons.