You're right about how "useful" needs to be defined. Monero at 30tps and blockchain growth rate is useless for global adoption. Lack of fungibility also makes every other cryptocurrency useless for global adoption.
You're also right that PoS is more sustainable than PoW, but I think this will change your mind: https://old.reddit.com/r/Monero/comments/lv5285/alt_take_on_...
It did for me. Thankfully since the energy consumption does not scale with the transaction rate, it's not a long term problem I think. Currently, the high energy per transaction stats are only because the adoption is low.
You're also right that PoS is more sustainable than PoW, but I think this will change your mind: https://old.reddit.com/r/Monero/comments/lv5285/alt_take_on_... It did for me. Thankfully since the energy consumption does not scale with the transaction rate, it's not a long term problem I think. Currently, the high energy per transaction stats are only because the adoption is low.