Being a captain for so many years, Dhoni could have very well played at No 4 in T20I's regularly or any format for that matter had he was greedy enough to consider his personal milestones more important than the teams cause but rather he chooses to bat at the most difficult position say No: 6 or No: 7 considering there was no other reliable or better options for India. Either most batsmen in India are Top order batsmen or they simply didnt have anyone as reliable and as consistent as Dhoni at No 6 and 7 with the finishers role.
I very well remember when he batted at the top order or when the top order was dismissed early he always scored big runs. But the most important factor of Dhoni's carrier is he did the tough job by scoring most runs at the death specially when the ball becomes old, soft and its not as easy to score runs with a hard new ball specially in the powerplays.
And as far as ur criticism of him scoring more 50's for CSK, he had the liberty of batting higher up the order considering he always had good strikers or finishers in Albie, Bravo and others to share his burdon. But that was not the case with India. Yuvraj and Raina at their prime did try helping Dhoni but they werent as consistent as Dhoni himself. So he had to take the most important and tougher role. I surely believe u will surely understand the value of Dhoni the finisher specially considering the possible replacements in Rishabh Pant and Ishaan Kishan are all top order players.