How big is the 'trustless' part of the ecosystem? 5%? 1%? Most of the speculation happens on centralized exchanges which very much involves (completely unjustified) trust.
Googling, it seems that the best estimates seem to indicate between 2 and 4 million Bitcoin are permanently lost (lost keys, known hardware failures of failed wallets, unclear if this counts Satoshi's million bitcoins or not). This estimate [0] by an analysis firm who appears to be broadly pro-crypto suggests 3 million lost, and that ~14.5 million BTC are "illiquid". Illiquid obviously doesn't mean lost
Illiquid doesn't mean lost, but it suggests something to me about the current conversation. If only ~4.5 million BTC are even a little bit liquid, then it's fair to say that at least half the engagement with BTC in balance terms is on exchanges, and probably more considering velocity of money. Not the grandparent's claim of 99%, but also not your claim of 10%. At the very least, not an obviously settled question.