letsgetrealLet's Encrypt allows anyone to have secure https communication, sure, but it doesn't address the question of website authenticity. I groan when I'm on an e-commerce site and I click on the browser URL lock icon and see a Let's Encrypt certificate because frankly anyone can create one for no cost and I don't know if it's the real website or if I made a URL typo. Say what you will about the expensive cert providers, but it's reassuring when you see DigiCert or Sectigo - with a company name and the address of the head office.
It was never a reasonable goal of the WebPKI to authenticate entities; only to help establish end-to-end encryption between unrelated parties on the Internet. The WebPKI can ensure you're talking to whoever controls `ycombinator.com`, but it has to be up to some other layer of the security stack to decide whether you want to be talking to `ycombinator.com`. (This is in fact part of the logic behind FIDO2 and phishing-proof authentication).
FIDO2 doesn't solve the first website contact trust problem - only the HTTPS certificate does that.