Why was it so easy to defeat Toneri, Kinshiki and Momoshiki? Toneri had somewhat the same Goal as Madara. Madara gained Hagoromo's Power and Toneri, Hamura's. The both powers are, I believe equivalent.

Sharingan >> Rinnegan = Byakugan >> Tenseigan

He who awakens the Rinnegan, shall receive the Powers of Hagoromo and he who awakens the Tenseigan shall receive the Powers of Hamura. Which is exactly what happened. BUT... Toneri had the Power of Hamura, who has the equivalent Power as Hagoromo... Then, how was Naruto able to finish Toneri's Tenseigan (and the Powers of Hamura) away with one blow?? + just in Nine Tails Mode, without his Six Paths Powers.. It just doesn't add up.

Now.. let's move to the Movie Boruto:

Kinshiki and Momoshiki are very powerful beings... Momoshiki even has 3 Rinnegan (One in his Forehead, and one in each palm) and has also the equivalent, if not greater Power to those of Kaguya.... how the hell was he defeated by only Boruto (a child)? While it took Naruto &amp; Sasuke to seal away (not defeat) Kaguya and they both had the Six Paths Powers, while Boruto had none whatsoever.
Naruto and Sasuke during Boruto saga are way stronger than the version in the war arc, so any actual threat that is Kaguya or even just slightly above her is not gonna do much against them and did so because they were nerfed in the movie. 

As for how Boruto's rasengan finished the enemy is because Naruto used his chakra to charge it and you can expect that his rasengan is going to be over powered. 

These are reasons I believe so, as you can't expect them to be same level when they fought Kaguya as they did not have experience with their power and it's already shown in this series and many other that you become more powerful as you grow older until certain age.