As the sibling comment states, it's not stored as plain text.

You're right that external storage lets you use it elsewhere, but IMO using keepass has a lot of friction I personally don't mind but wouldn't initially recommend to most people. Browser password storage fills 99% of most people's needs.

They did at one point but not anymore. But either way any password filling is as secure as plaintext since it's pasted as plaintext, and you can just edit the DOM after it's filled.