What possible benefit does it have other than security?
Well, one thing is that it keeps us native to a $6B marketcap currency, enabling people to trade directly with that currency and settle using BTCPay. If we move away, people will need to use BTC tokens backed by an issuer instead, which adds a layer of counterparty risk.
That's exactly the problem
2-way peg tries to solve: having a non-issued interface with bitcoin from an outside chain.
You can also coinswap with other person as a shortcut.
Even Satoshi himself thought PoW was an inherent weakness of the bitcoin protocol.
Link please?
I can give you this one where he proposes merged mining to have multiple chains with different rules and uses:
https://bitcointalk.org/index.php?topic=1790.msg28696#msg28696Some more history to learn from:
http://forum.namecoin.info/viewtopic.php?f=2&t=1551