Baseless. Sabo was up against greatest force of WG who he thought was going after his brother after finally reuniting with him.
Sabo does not have island level or even town level feats to suggest he would have the ability to sink Dressrosa.
But the little updates of the "fight" show Sabo using a lot of AoE and effort and struggle, whereas Fuji looks like he just takes it.
Even his gravity attack was just a small preview, so he could pretend he tried
Entire surroundings is covered in fire just from the by-effect of the battle, compare that to Ace vs Blackbeard which, besides Flame Emperor in the end, did not cover the surroundings like this in fire, not even after Hiken
And in the panel you can see Sabo already battered and huffing and puffing, without Fuji even getting serious
Best bet for Sabo is Y1C, meaning he can survive against full fledged top tier for a while, but does not pose a credible threat to any of them, at least not yet, we will see what Oda has planned for him