Well, its a stop gap solution for sure but let me state my case -
Pant's keeping is very mediocre as well and he hasn't really looked like scoring any runs. I don't think he has the technique to withstand the Aussie bowling attack in these conditions. Every time he has scored runs its been on very flat batting tracks. I also don't see him succeeding in New Zealand or South Africa. Not sure he is the future basically. And Parthiv at least will put a price on his wicket. He might not score hundreds but he has repeatedly shown that he is good for 30 to 60 runs. Vijay and Rahul are walking wickets right now.
And playing Parthiv basically gives India the option of either adding an extra batsman down the order for insurance or playing that extra bowler if the pitch is flat or Hardik Pandya without sacrificing Hanuma Vihari who I believe India should stick with and not discard after just one game.
I am not convinced with this theory of sending Parthiv as a stopgap opener. In the past India has done this whenever they had struggled with limited success. Considering the success in the Perth, Australia will try again to produce a wicket with pace and bounce in both Melbourne and Sydney, even if they are not traditionally those wickets, they can still be altered to some extent to make them as close to the Perth wicket.
Parthiv's highest score in SA was 19. He is not the type to hang around, he loves playing his shots and might make good 20 or 30 but will eventually fall. His Wicket Keeping is average at best and even though Pant is not great with his WK skills, he is still young and can improve over time and hence it makes sense to invest in him.
India has been lacking a solid start at the top.
Even if that means a really slow start to get the ball old and reach the lunch without much damage.
I remember Aakash Chopra in the past has done this Last tour Vijay was successful in a similar role.
So top 3 in my opinion should have tight technique to handle the new ball on a difficult wicket.
From what I have seen so far, Vijay, Pujara and Vihari have the technique to grind it out.
This will allow Kohli, Rahane, Rohit/Pandya and Pant to play their naturally aggressive game.