There is no one else on Wano who can beat BM right now, unless you think Kid > RS Sanji, Judge, Ichiji, Reiju, Niji, Yonji combined.
If the Navy showing up(and they will judging by the hints), their is no point of the Germa66 beeing in Wano. Also I don't believe either that Kid could stall or defeated Big mom. Judge was easily trashed away,Big mom use three of the 5Germa66 soldiers as fucking toys.
Neither going even all out, Big mom is a total different lvl and she would still trash them. Or do you believe that guys like Nami,Brook,Ussop,Chopper and Robin can stall someone as Doflamingo/Katakuri in a battle,because the gap is such large.
Is the Germa66 a good and strong army overall for the war? Yes they are, but can they stall serious Big mom? I don't think so, if Oda ever would bring the Germa66 to Wano, I would more believe they would more helpful in the battle against Big mom soldiers.