Looking at last 5 years is not correct (responding to sibling comment for this para). It is very short term and does not cover the time periods when India does not grow. Back of the envelope calculation shows a 10 X growth over past 20 years which averages to about 12% returns. Give back 5% in rupee depreciation and we are talking about 7% in USD terms.
But it comes at additional cost. Accounting costs. You need to file taxes in India and you need to claim its credit in US. Extra paperwork both sides. Foreign tax credit is not 100%, it is close enough, but you lose small change claiming it back. Then there is lag in selling something and being able to use that money in USD. You need to fill forms, get CA certificates and work with banks to get money back, takes time and takes money to get that done. Maybe the incidental costs are 0.1%, maybe they are 1% if you start counting the time you spend.
Also we can not compare returns directly against Indian equities. I will need to look it up but I believe some stocks are locked to the maximum for foreigners (maybe at 50%) so you can not buy any more unless a foreigner sells ... although the number of such stocks may be limited, if you can not buy and sell like an Indian, your returns can not be comparable. They may incidentally come out better, or they may incidentally come out worse.
In my personal experience working with 3 advisors (all companies managing thousands of crores = close to a billion dollars //* should cross check *// of total client funds), my returns never matched their benchmarks, and there was always some explanation, but never a match to their company wide returns for all clients.