To be honest, by manga-wise timeline, it was not really that long since the last time Sanji & co. were shown facing Big Mam's ship. So much things happened in Dressrosa which made up for the 10+ chapters after that yet the time hadn't passed much. Sanji's team was (supposedly) in deep trouble with a Yonko, still, Sanji showed no fear to commit some counter attacks.
However, i bet there was a reason why Oda chose Sanji out of the Monster Trio & co. to be with the Sunny's group.
It was the same case back in Punk Hazard, when the Strawhats did the draw before exploring the island, Zoro, Robin and Usopp were selected to keep Luffy company plus Sanji was destined to guard the rest of the members.
Made me thought that Luffy and Zoro for frontline battle, whereas Sanji was the opposite. Both positions are important, front and back. There's a possibility that Sanji & co. will meet Jinbei at the same time Big Mam tries to launch an attack on them.