Sure, but mark-to-market is a commonly used method of valuing assets. Of course what you’re saying is true, but there’s nothing inherently wrong with valuing a portfolio like this. Even with real currency, you can’t directly measure value in another currency for the reasons you gave. So it’s probably just a better idea to ignore slippage and bid-ask bread when talking about value.
There is a difference though: Google isn't built on a scam. While another dot com boom isn't impossible, it's still not very likely that it will happen in the near future. So your Google cofounder with tons of Google shares can divest from them over a period of decades, building themselves a diverse portfolio. A pyramid scheme currency only has very short lived and temporary value. Thus you need to exit before the scam is detected. The faster you try to exit though, the more the effect that GP mentioned becomes relevant.
Anyways, even if she had managed to exit with a large stash of money, she'd still have to keep it out of reach from the government authorities, lawyers, etc. So even if she owned $1B momentarily, it wouldn't be of much worth to her if she (rightfully) lost it all again in 4 years plus interest. That's why criminals have such an extravagant lifestyle: they can't think long term because long term they might be in prison, killed by another criminal, etc. Same goes for rich people in authoritarian regimes: the moment they fall out of favour, their money is gone, so often they want to get it out of the country before the tides turn on them.
