It’s designed in at the base level — that immutability is a feature for most proponents: if you don’t have it, you’ve just paid a lot more for a very slow database.

You're operating under a binary understanding. Forks are the very obvious proof that what you say is wrong - they are a primitive way of settling disputes but a good starting point none the less.

Token governance is the next step from forking that isn't so arduous. With proper governance, the community around a token can come to a consensus that a mistake led to irrecoverable funds (for example) for one user and if the amount is worth the time issue a proposal and vote on minting replacement tokens for that user. Token holders are the share holders of their protocol, no reason all the normal operations that make a business safer for users can't be implemented in token contracts.

Try not to confuse the current state with what's possible.