Arbitrage traders are not platforms or service providers. There will be a slew of arbitrage traders ready to charge a premium to swap out of sBTC, but they are not 'service providers'. They are not trusted, centralized, or able to interfere with your exit from sBTC. Anyone with a little money can become an arbitrage trader, so there will be many traders competing for volume, so they wont be able to charge too much of a premium or risk losing business to the other arbitrage traders.

Yes, sBTC -> BTC pressure may build, and arbitragers may charge a premium to exit, but if that premium gets too large, it will invite more liquidity into the market, and cause the premium to drop back down.

This is much more desirable than the trusted mint/provider situation we find ourselves in with Lightning, Cashu, Fedimint, etc