"Also these relays, clients etc that offer nip-5 to anyone willing to pay for it basically makes it meaningless."

That right there has always been my biggest problem with NIP-05. My understanding of what NIP-05 was meant to represent was ALWAYS old-school Twitter verification. But people who hand out these free addresses keep saying no it's not for verification but it's meant to be a Human-Readable Identifier like an email address or any other user@domain identifier. And because that mindset is so prevalent, that's what the NIP has morphed into.