If they need legally valid information, they can subpoena the registrar. My phone number and home IP address also don't have a name, address, and email address attached; if someone wants to find who's behind a number, you need to have a reason which a judge will check (or perhaps a public prosecutor depending on if the operator is buddies with the police and it's a criminal offence). Would be kind of crazy if every website you visit gets your full details and can start sending advertisements or harass you for posting something they didn't like. Same for a domain name
And that's besides the point that the registrar doesn't check this information. If you wanted to lie, they're not stopping you from getting false info into whois (or any alternative)
If it needs to be authentic, then DNS does have signatures nowadays, or a delegation as iirc you mentioned already. I just don't know why it should be more authentic than the unverified information that's currently in whois
