• Use of the API is unsafe. - Yes.
• An improved alternative API is available. - My understanding is that the WHATWG URL API is supposed to be the improved alt API, so I'll leave it checked for now unless anyone has any objections.
• Breaking changes to the API are expected in a future major release. - I guess that depends on whether we will proceed with the deprecation, so I guess it's undecided for now?

Since at least one of the points above holds true, it should qualify for a deprecation, but hey, the deprecation status was previously revoked and it was moved to legacy status in #37784, so I'm doubtful that it would be that straightforward. I don't know why the deprecation was revoked but it would be nice to know the reason and if it still applies, we should update the doc accordingly.

cc @nodejs/tsc