I don't really fundamentally disagree with what you said but did you answer the question? "enlighten us how the security of the network holds if we lose mass miners?"
Aye, I did. Network security is a cost of entry item. It is a contributing element in determining if a coin is worth nothing or more than nothing. If network security does not exist, then the coin is not viable and is worth zero. So in that sense, miners have a very important role to play. But alas, they cannot positively affect value outside of the 0 or >0 effect I have previously described for the reasons I have previously described.
In reality it takes both sides to mutually agree on a price and both sides set the price.
I appreciate your argument, here - that whomever places the order, be they buyer or seller, sets the price at which the transaction occurs. While this is a microeconomic interpretation, I certainly cannot disagree that supply & demand effects ought to be considered. But here's the sticking point when it comes to minable cryptos... because miners can create coins out of essentially nothing (their costs of acquisition are sunk out-of-market), supply will continually meet or exceed demand while a coin is still in its PoW stage. And that fact necessarily tilts the supply/demand element in favour of supply, meaning value is determined only by what the market will bear. And "what the market will bear" means the exchange rate a buyer is willing to pay for a coin, not the rate at which a seller is willing to sell.
I apologize for dragging you and the thread OT. Please feel free to respond to my rebuttal if you would like, but I pledge to not pursue the debate further in this milieu.