That isn't what it's for. You can assume the government (really any government) has control over at least one CA. What Let's Encrypt does against state-level a

That isn't what it's for. You can assume the government (really any government) has control over at least one CA. What Let's Encrypt does against state-level actors is let people easily use HTTPS instead of HTTP without subjecting their users to self-signed certificate warnings. A government could still MITM the connection but that requires an active attack rather than passive surveillance. And active attacks are subject to detection. So it protects against undetectable mass surveillance.