I legitimately think Oda has Kizaru and Saturn doing nothing because there's no one that can oppose them currently, Sanji can't, so instead of trying to create unrealistic scenarios of Kizaru and Saturn being stalled, he is just waiting and leaving them free.
Even then, he didn't even thought of making Jimbei and Sanji fighting Kizaru together, but chose to do the complete opposite, it's the Luffy show.
Even then, he didn't even thought of making Jimbei and Sanji fighting Kizaru together, but chose to do the complete opposite, it's the Luffy show.