Stam, thank you for your response! Yes, I meant k=0 & spatial part is flat. I see the connection in your reference, but presented via different approach...
If this fact is not new then why the correspondence of the Schwarzschild-de Sitter to the FLRW with central gravity is not such obvious problem? I red that Einstein tried to solve it, Gilbert and McVittie and there are still debates on this nowadays..
That's just history. This has now been resolved-just read the lectures linked to; more details can be found here: Article Lecture Notes on General Relativity
or https://kpfu.ru/portal/docs/F1110497646/Starobinsky.pdf
What's ``obvious'' and what isn't doesn't mean anything-it's personal opinion, not a technical, impersonal, statement. What matters is that the mathematical procedure is, now, well understood, so it's better to skip history and focus on the technical aspects.
Section 8 has nice explanation on the correspondence of the FLRW to de Sitter for isotropic and homogeneous Universe. But there is no single word on the FLRW with central gravity (FLRW + Schwarzschild).