More than that, a block cipher is a keyed permutation — that is, many permutations selected by the key, soooo by fixing the key we can have an unkeyed permutati

More than that, a block cipher is a keyed permutation — that is, many permutations selected by the key, soooo by fixing the key we can have an unkeyed permutation and use it for sponges! Or... BLAKE2 uses ChaCha permutation, but includes additions of key words to turn it into a block cipher, and then uses this block cipher in a MD-like construction. Metamorphosis... Of course, if you take some block cipher, fix the key, and make a sponge from it, nobody guarantees that it will be secure. Just like trying to build a block cipher from some permutation will not result in anything good. So it's not on the same level as building higher-level secure things (such as PRNG) from a primitive. I think what I'm trying to say is: in crypto you can indeed build many things from other things.