While I'm not a fan of how the Ethereum project and ETH token is managed, Solidity programming language brought real financancial innovations in trustless contracts.
There is a real possibility of BTC finding home on Ethereum network in future. Recent advancements in cryptography make building of fully trust-less bridge between two possible, without requiring any changes on Bitcoin side. So possibility will be there. As for the need - there is no indication of Bitcoin moving towards solving time-bandit attacks. They will become a real issue once block reward falls. I'm skeptical that Bitcoin as a project is even capable of solving this problem. It would require additional emission of BTC, and "21M BTC meme" is way too strong.
The real enemy is the closed fractional reserve banking system, I think practucally any open source cryptocurrency is better than that.
~89% of bitcoin have already been issued. Yes, they will continue to be emitted for a long time, but at a rate that is rapidly approaching inconsequential.
Try asking $100M for a short time from any bank, I'll see how successful you are.
Last time I checked defi usdt lending rates seemed to hover around 8-9%. Not that exciting when you consider insane gas fees and all the hassle managing the contracts.
Nanoseconds of computational time.
If the trade isn't possible then the transaction fails and it doesn't go through at all. You pay the transaction fee.