What you said it's correct when the team play in away pitch they will struggle to play. But in this series SL is a too worst team this is the truth we have to accept. There is no comparison b/w Indian team players and SL teams players. And from last 1 year India is performing well in away grounds so i think India can give good fight to SA in next series.
In 2017, Indian went mostly to Bangladesh, SL and WI. They went to England for ICC Champions Trophy but lost a match to Pakistan team. They are mostly playing in Indian pitches and that's wins are more but if they go to Australia, SA and NZ then we will come to know this new talent how they can play on fast tracks. But surely Indian team is much stronger than SL team.