After the first match bravado, it was only fair that Indians failed in every department. 
The likes of Arshdeep and Avesh already took enough wickets in the first match and it's okay to go wicketless in the final match as well lol
I think they were in a relaxed mode and played with a bit overconfidence after winning the first match very easily. I'm not going to blame the bowlers though for today's defeat. Indian players haven't batted well today. As an opener, Ruturaj Gaikwad isn't doing well in the ODI format. Some Indian player plays a lot better in T20I and IPL matches, but their performance isn't good in ODI format as expected.The likes of Arshdeep and Avesh already took enough wickets in the first match and it's okay to go wicketless in the final match as well lol
Proteas just outplayed them and there is no shame in accepting this. So far Rutu is not clicking but he's just 6 ODI old in this format and deserves a long rope because you want at least 4 good openers (including bench strength). Gill and Jaiswal (WIP) are almost set, need a couple of more guys at this slot.