I think about it this way: if I get a 20 dollar paper note let's say in 1810 and believe it to represent 20 ounces of silver (simplified to make the point) but upon visiting my bank branch I only find 5 ounces - the bank is insolvent and the paper notes immediately near worthless. In the crypto world 5 filecoin will always be 5 filecoin- and I can see (and trade in and out of them) on a 24/7 basis. That's quite a different trust level to me. In fact I can 'shapeshift' them into hundreds of other coins that I deem more relevant or worthy as a value store at a moments notice. Does not that sound like a superior system, even when granted, it's not perfect (as long as we are dealing with imperfect knowledge of the future and human emotions)
This seems to reinforce the analogy rather than rebut it. Your coins can still very suddenly go from being worth X worth of goods or services to .01X. It's maybe even worse with crypto, since the only things you can currently buy are dollars or other coins.
The ability to "shape shift" your declining currency to better ones assumes you can out-speculate the market in knowing when to exit, and which coins to buy.
But it's still not backed by anything, it's still potentially worthless the moment you go to cash it in - you have a better idea of that potential, sure.
And maybe filecoin is an exception - most ICOs seem a little scammy at best, with value based purely on speculation and scarcity.
Bitcoin and other crypto-coins are also created without the gold or silver backing of course... they just aren't issued in quite the same way.