Checking the USDC to INR rate is one thing; sending money is another. Grey adds three costs to a transfer, a deposit fee, a conversion fee and a send fee, and shows every one of them with the exact rupee amount your recipient receives before you confirm.
Because Grey does not add a margin to the exchange rate on top of the stated fees, the figure to compare is simple: the exact rupee amount for a transfer from USDC to INR, shown before you confirm. Grey pays out in rupees inside India, to a bank account number with its IFSC code or to a UPI ID.