How do Naruto and Sasuke manage to beat Kaguya so quickly?
This fight within the narutoverse is one of the few examples where a team made a huge difference other than a one on one fight . Hagoromo and Hamura took months to defeat kaguya . On the other hand Naruto and Sasuke were with sakura , obito and kakashi ( one of the most revered shinobi in narutoverse). also one of the other major reasons she was defeated was because of the tailed beasts themselves .

Kaguya herself was fighting after thousands of years , She had a massive chakra even greater than madara as sasuke confirms . She was continuously teleporting between dimensions which was consuming huge amounts of chakra from her . Black Zetsu although made a plan of separating them , and did so successfully . Obito successfully bought him back with the help of sakura . Although you say that sakura just threw a punch and there were some kamui's by both kakashi and obito what you forget was how they came at absolutely crucial moments . Obito gave up his life to save both of them from All-killing ash bones of Kaguya . 

The major turning point within the battle came when kaguya got hit by the Naruto's Rasenshuriken . Taken From Wikia[Naruto Shippuden]:

 After getting hit by Naruto's tailed beast powered Rasenshuriken, the Ten-
 Tails' chakra within her reacted violently to the chakra of the other 
 tailed beasts, transforming her into a rabbit-like chakra monster, which 
 according to Black Zetsu was a form she couldn't control. 


Now the battle went downhill after this , when hagoromo and hamura fought kaguya there was no concept of the tailed beasts being separate , but during these two thousand years they had spawned from the ten tailed beast and had gained experiences and fought in wars . so when naruto hit her with the rasenshuriken , she was in the unstable state wherein she was being attacked both from outside and inside [ the tailed beasts started resisting there capture] and it was soon after this weakened moment that they were able to seal her . Although she tried to escape , there came in sakura's opportune punch to stop her from this and they successfully sealed her . 

Another thing you need to be wary of is the war itself took only within two days .