most new PoS chains do just fine because validators are owned by VCs that want to grow the network. whether they can successfully decentralize is an open question but the bootstrap problem is solved
it's solved if your only holders consist of trusted parties, which is a trivial (but unrealistic) solution to a lot of crypto problems ;)
it seems entirely certain that cryptos that are not VC backed will launch in the future. It happens almost daily actually.
this is a stronger guarantor of safety than PoW for every chain aside from ones that dominate their computing platform (BTC/ETH). anon miners will eat a naive network and move on.
And if you are requiring trust between parties... you might as well simply have an auditable database instead of requiring staking or mining at all.
(requiring oracular knowledge (external to the system) that other VCs have a financial stake is still a trust-based system... and they could still sell that to someone who doesn't, and fuck you over, and your knowledge that they won't do that for social or contractual reasons is still oracular knowledge. You haven't solved anything, you've just created an oracle that everyone agrees to trust, which is a trivial solution to almost all challenges within crypto.)
"it's actually impossible to start new networks from scratch based on proof-of-stake" is simply incorrect. almost all crypto networks will start this way.