That makes sense, Rikudou was foreshadowed in manga, but his relatives - not even once (aside of sons), without Kaguya and her second son (aka plot twist for The Last) it could be done much more naturally and well suited in story, just like NS ending... oh wait, that's mean logic... silly me 
All of it was just thrown together as quickly as possible with as little to no explanation as possible.
Yeah but I feel like it went a little too far with the Rikudou. I didn't like that his role was basically to give a history lesson and free powerups for Naruto and Sasuke, plus I felt everything about him and his family was really forced at the end there. Now that I know more about him he's completely uninteresting, same with the rest of the Otsutsuki clan.
It did went way too far with him and yes it was forced. In the end a mysterious figure that save the world ended up being an old fart that keep saying his time was up and also he was incredibly stupid. He asked Sasuke what he wants to do, Sasuke tells him that he wants to kill Naruto and the Rikudou gives him the power to do it.
That's like having two sons and going to them and asking them:
Dad: Hey son what do you want to do in the future?
Son 1:Well dad I have a lot of friends and I really want to protect them.
Dad: Ok son here's a gun to protect them. But be careful only use it when you need to protect your friends.
Son 1: Thanks dad.
Dad: And you my other son, what do you want to do?
Son 2: I want to kill my brother aka your son.
Dad: Ok my son here's the gun to do it.

Which I've told you - time and time again - is dangerous! There will never be consensus, son, among those you have helped to ascend. They will all differ in their views of what it means to be free. The peace you so desperately seek does not exist.
These men are united now by a common cause. But when this battle is finished they will fall to fighting amongst themselves about how best to ensure control. In time it will lead to war. You will see.