One thing cryptography solves in web3 that I haven't seen any recent alternatives for is decentralised identity.
You don't need blockchains and other such cruft for a simple signature system, but there's nothing on the web that actually makes use of such a system except for some government systems or intranets. Currently, every website asks for an email address and a username, but for most people that email address can easily be taken from them. This is especially bad for services that work with "magic links".
WebAuthn and now FIDO2 may soon fix this problem, tieing your base identity to a cryptographic key, either in hardware or software, with email as a mere recovery option if the worst were to happen.
As for an answer to your question: use the core protocol to generate speculative value through hype and pyramid schemes and cash out big time in a bigger-sucker scheme before you're found out.