Well this simply isn't true. You can only upgrade your infrastructure so much but air-mobile arty guns will always be the king of the battlefield. You don't think being able to transport 155/52 calibre arty guns wherever you like is a nice capability to have and a pretty devastating one at that?
A/C will obviously operate in airspace where safe flight ops can be carried out. Considering arty will always be a few kms behind the frontline this isn't a real issue.
Comparing Apples and Oranges, the M777 fills a very real niche and thus comparing it to the FH-77/Dhanush is silly to say the least.
This gun is not 155/52, its 155/39...
M777 does a good job for being a ULH. But My point is that when Armed forces are being asked to prioritize procurements because of lack of funds, this 700 Million dollars could have been better utilized.