>>280494915
Garp went there SPECIFICALLY to fight Roger, the fact that he needed to join forces with him implies that Xebec was too strong for either of them. Garp doesn't care about the Celestial dragons, but Sengoku knows this, he's just saying that Garp could not accomplish what he went there or do.

Also Sengoku reffers to Rocks as Rogers "Greatest Foe" after all these years, despite Roger regularly fighting Whitebeard and Garp.