I don't think being an Indra or Ashura affects learning Sage mode, if that was the case then there be no other Sage mode, yet we have these Sage mode User:
Jiraiya although not perfected
Minato perfect but can't hold sage mode long
Kabuto perfect
Pain used his rinnengan to absorb Sage mode Naruto, but because of his inexperience Pain turned to a frog statue
Madara used his rinnengan to absorb Hashirama to make Sage mode his own, no draw back, we don't see Madara ever lose Sage mode till Kaguya spits him out and then dies in the end
Sasuke has plenty of experience with Senjutsu thanks to Curse Seal, it has nothing to do with absorbing, but it has everything to do with control Curse Seal which is basically controlling Senjutsu. Those who can't control the Curse Seal either dies or explode.