Dhoni has 2500+ runs outside of India at avg of 54 and SR of 88 when he batted 5 or above. Why not make a list of all batsmen with these kind of criterion and see where they stand?
If you genuinely think that Dhoni is not good outside of India then here is entire list of batsmen outside of home to make a apple to apple comparison.
Here are all batsmen in entire history who batted 5 and above( Dhoni didn't bat much above 5 , but let's take everyone even if they batted 4,3 or so on...)
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If you think only ton matters then we can pull a list of batsmen who batted at 5 and see how many have 5+ tons at position 5. If some one is batting at 1-2-3 then they will have lots of tons but that simply a function of batting higher up.
Dhoni is surely better in Asian conditions, no doubt about it, but his stats would have been inflated if he had batted higher up when it comes to runs/tons. It's a simple logic.