To me all it shows is that Oda wants to ends One Piece faster than expected.
In not a single world, would garp, a rival, on equal foot, with WB and Roger, or close enough to not be different, end up as he did.
Getting basically killed by a mere admiral level character, followed by a bunch of high tiers at most. Basically shishibukai level characters.
Now compare it to Old and SICK - emphasis on sick - white beard, who was so sick that he couldn't use HAKI :
He beat up everyone on his sight. Akainu? Black beard? so on and so forth, without even using HAKI. He died out of sickness. That's it.
That foreshadow a sad fast ending for one piece.