Premise of this thread is bullshit. I seriously doubt Kishi is crazy/stupid enough to introduce single character "greater then Kaguya". Keeping that in mind either Kishi through Sasuke was just hyping up villain or maybe he meant a lot of bad guys like army of minions who together with Bald guy would be even greater threat then kaguya. Of course not in power but harder to stop as they may spread and attack on bigger scale while scattering to different places. They may even keep attacking Elemental nations and hide so they can not be found. This would be worse then Kaguya because Neither Naruto or Sasuke would stop deaths of people which finally would lead to chaos among people.
The purpouse of army at first time was to nullify any possible opposition Kaguya would get, that for first. Second She wanted to have them under control so there will not be war anymore.
The purpouse of army supposed to be created for second time clearly to destroy/force Hamura along with Ootsutsuki clan to give up and join her or just beat her. Why ?. In the last the movie it was explained that Hamura agreed to go with Hagoromo's plan for peace and spreading chakra even although he didn't agree fully. Keep that in mind Hamura who was leader of Ootsutsuki clan after Hagoromo's decision to stay on earth would clearly oppose whatever Kaguya tried to do.
Kaguya knowing that she once lost to both Hagoromo and Hamura in monster form, learned from her mistake and tried to create army to aid her or if they were useless feed her chakra at least.
The Bald man is most likely one of zetsu created in Kaguya's first army taken by Orochimaru and he most likely was experimenting on them for long time being able to infuse Uchiha dna about which he has obessesion inside that Zetsu.
Shin's kid version are most likely also First Zetsu who were smaller version ;p. They may be inperfect copy of in compare to Shin's old version.
Just my thoughts
