Why use Monero's future L2 if blocksize is dynamic & can adjust to any demand?

There is no exchange risk when swapping between BTC tokens. Liquid to LN swaps happen in the background when you make a txn from a wallet. So if someone doesn't support Liquid they get a LN payment instead. There will be similar bridges to everything else & LN forced closes will mostly be LSP problems, not average consumer level issues.