the value of a cryptocurrency often reflects ...
The price of a cryptocurrency reflects those things. It's value is zero. Period. There is nothing behind it.
While they are not backed by tangible goods, neither are fiat currencies or many derivatives
No, fiat currencies are backed by debt, meaning that real people and companies have made enforceable legal commitments to do real work to generate the value backing the dollars or whatever. Without getting into the details, every time a dollar is created, that creation is balanced by the creation of a dollar of debt, the commitment of some productive entity to produce value to repay that debt (and thereby destroy that dollar). As a common example, when you borrow money to buy a house, the bank doesn't lend you money [*] that other people deposited, it creates that money out of thin air at the same instant you sign an enforceable contract to repay it, meaning you commit to do some sort of value-producing work to generate the value of those dollars.
Derivatives represent specific legal contracts to perform some action, e.g. buy a fixed amount of stock from the derivative seller on or by a specific date for a specific price, and those contracts get their value from the underlying security. That underlying security can also be some sort of contractual obligation rather than a hard asset, but if you keep digging down the layers you always get to something real. It's always possible, of course, that the layers of repackaging make the actual value hard enough to see that its price becomes divorced from that value (and stock pricing also gets divorced from underlying value to various degrees), but at bottom there must be something of actual substance. Further, if markets were perfectly efficient, it would not be possible for the price to move away from the value.
None of this is true with cryptoassets. Their true value is zero (arguably, negative, since proof of work is a pure sink that generates no utility), so any price above zero represents market inefficiency/insanity.
[*] It used to be that the bank created most of the money under the fractional reserve system, but for quite a while now most of the developed world has abandoned the reserve lending requirements, enabling banks to effectively create all of the money they lend. This might seem like a crazy system, but it's actually pure genius because it allows the money supply to expand and contract with the economy, which along with Keynsian fiscal policy massively reduces the boom and bust cycles we regularly experienced before we switched from metallic to fiat currency.