I don't think so, because Shanks says he was born on an island in West Blue.
Yes and that's the flaw in that theory.
I still believe it to be a good theory, I do think Shanks being a CD is the most plausible cause of his appearance in Mary Geoise, just...
Maybe Shanks isn't a legal child. Typically Pirates have no parents...
But I also don't think it necessarily has to do anything with the Rocks Era being 38 years ago.
Rather I think "saving the CDs relates to whatever conclusions can be taken from lost history. Think about it, the Riu Poneglyph won't just be: “The CDs did bad stuff, they are evil". We already know that, no one needs to find out. There is going to be a twist, something that throws you off your chair, something that needs "a conclusion", something that has possibly to do with "the right time".
I think Xebec might have actually found One Piece or an Ancient Weapon, drawn the wrong conclusion, and thus needed to be stopped. Having Kaido, Linlin, Newgate, Shiki and other famous Pirates under his wing, Xebec already is a proto-pirate king, meta-wise.
Think about it, why do Linlin and Kaido know about Road Poneglyphs despite being unable to read them? Linlin had hers before Roger...
And why did Roger even search for it in the first place, where did he get the idea of One Piece from, if everyone now got this idea from Roger?
Would explain why God Valley has disappeared, it was destroyed because Xebec left his secret there.
If Xebec is Blackbeard's role model that would explain the weird archaelogy hobby.
Blackbeard tries to find something because Xebec found something.