I don't really get it. As far as I can tell, a coin that uses something like, for example, proof-of-spacetime is just going to push the resources "wasted" to whatever's required to create hard drives: land for mining raw materials, metals, the energy required to create the hard drive and ship it, etc. Is there really anything better than proof-of-work?

> going to push the resources "wasted" to whatever's required to create hard drives

Not if buying hard drives to mine with is unprofitable. There are huge amounts of free hard drive space already paid for. If a nontrivial fraction of that is used for mining---at negligible cost---then commercial mining may find itself unable to compete.