Imo, when it comes to Shanks/BB, these are things he won't avoid.
For sure, a lot of what I currently call One Piece's "second act" (Hody, Caesar, Doflamingo, Katakuri, Big Mom, and Kaido) are a very weird time for the series. 5 of the 6 villains weren't really set up prior to the timeskip, save for Doflamingo (who I felt was the most fleshed out one).
Now as we head to what Im considering his 3rd act and probably his "biggest" Saga, I personally don't see him short changing Shanks, Blackbeard, Dragon, Kuma, Admirals, WG, etc, because all of these characters are from the earlier parts of the series. For sure, things like Weevil or Im or Rocks are newer concepts, but I think they all have implications to currently existing characters anyway.
Vegapunk is practically an exception, because he's been referenced since Water 7 and seems to have his hands in basically every single major arc since (Mentioned in Thriller Bark, Sabaody, Marineford, Punk Hazard, Dressrosa, WCI, and Wano).
Idk I'm pretty confident that Oda won't flunk out on what are presumably his favorite characters (we already know this is the case for Shanks and Buggy). A lot of this is just pure DNA for the endgame anyway, however many arcs there are left.