I think most people don't understand that if your prices shoot up so high that means your bankers underpriced it too much and their clients made a boatload and the company missed out.
So pre-IPO shareholders still get most of the upside. $250 million to the float, $2.2 billion to the rest of the shareholders.
It can still be a mispricing, but it isn't so drastically painful if you look at it that way.
The calculation for if it's better to sell the other 90% into a hot market would be: 40% of 10% is only 4%. So if the initial pop has a long term positive impact of 4.4% on the price, then the existing shareholders come out ahead.
It's debatable, but I think there are two sides.
The other misunderstanding is that a company splitting shares doesn't increase the value of your position.