It's not like Gunko is as powerful as Saturn (One of Saturn's moves lowkey obliterated Warcury, who Luffy couldn’t even scratch btw)
But even then, Sanji definitely would've done something by the time being. He wouldn't lay there seeing Robin fighting someone she had no chance of winning, specially someone like Sommers who would piss Sanji off, much less seeing Nami complaining about stuff.
What draws attention on Jinbe here is that he is way too calm regarding the situation, Sanji would've went crazy at some point instead of seeing his crew in danger and kids being made hostages ready to get killed.
What really matters for Jinbe right now is what he does next, he needs to compensate for being so useless here. Sanji in Egghead, despite caught by Saturn's hax, it only happened once, them he pulled up some feats and savings after that (and prior to that btw).