First this is all hindsight now. We don't know the probabilities of this outcome vs. others. Figma's shareholders didn't at the time, which is why they chose to sell. Khan didn't either.
Second, 3x over two years isn't that much. There must be many opportunities in SV for all of Figma's employees and investors that could have given them a much higher return than that with much less risk.
I don't have this data, but one could look at secondary sales in the past two years as a measure of the increased risk and opportunity cost, right?
Any delay of people getting liquid impacts the creation of other startups, both by the Figma people who can now leave and do their own thing and for the companies Figma stakeholders would have invested in . This is super hard to measure but it is the kind of thing markets are good at measuring when they ask shareholders "sell now to Adobe or wait to IPO?"
This seems really good for Figma users, most of all. Most of the value destroyed by the acquisition would have been in the distortion and likely ultimate destruction of a company culture that made an insanely good product.
But those people are capable of going and making new products, and maybe Figma at its current phase is now too boring a thing for their talents, and should be managed by a more boring organization staffed by people who are slightly less able to make another Figma.
Who knows, but I doubt Khan (or any one individual or organization) is in a better position to assess the optimal delivery of what people want than the incentivized distributed intelligence of all the stakeholders and the people and markets around them.
Again, there are other reasons to do this that markets wouldn't quantify.