The opposite is true, proof of work is hopelessly insecure and centralized. It's hopelessly insecure because resources needed to mine are external - so any attack by the only realistic adversary (ie. a state) is always just a question of resources, and the most pessimistic cost is in low billions of dollars. Realistically - America could already 51% bitcoin by forcing regulations on existing miners for nearly zero cost.
It's also centralized because mining has infinite economies of scale. Bitcoin mining started with hobbyists mining on home pcs, now there are companies buying power plants just to mine. This only makes it easier for governments to control.
The only reason no big PoW coins were successfully attacked is because there's no clear motivation for anyone - nothing in the real world relies on any cryptocurrency to continue existing. The only realistic attack would be to try to exchange tokens on the attacked PoW network for tokens on another - which is easily done for low 9 figs, but becomes increasingly hard afterwards - making any attack uneconomical. On top of that there are legal issues - it's very possible a 51% double spending attack would be legally treated as theft.
This all changes completely the moment major countries and corporations go down if some blockchain goes down. Imagine Iran defaulting if bitcoin or ethereum gets taken over in a 51% PoW attack, with all transactions from Iran addresses censored. It would be orders of magnitudes cheaper than any serious military action. Fortunately for Iran and crypto holders that's not true. A significant adoption of a PoW network would end up in an inevitable disaster and potentially destroy any trust in cryptocurrencies forever.
Of all invented consensus methods only proof of stake can survive in a truly hostile environment. No government can print eth at will to take over ethereum, and stakers can easily stay anonymous, unlike massive corporate miners.
Bitcoin holders are very good at propaganda and pretending PoW is safe, which works as marketing, but wouldn't do anything against a real military incentive to take control over bitcoin.
>I'm much more bullish on Chia and proof-of-space/time
No, Chia has the same issue. Anything that relies on external resources as consensus votes is fundamentally insecure.