To be honest, Dhoni's card was marked once Zaheer Khan and Harbhajan Singh faded away. For along time both were key to India's success. Without Khan, India's fast bowlers are pretty much clueless. Singh at his best was better than Ashwin/Jadeja/Mishra put together.
Dhoni won 27/60 Tests as Indian skipper, but only 6/30 outside of India. Since the 2011 World Cup(both Khan and Singh's last hoorah), India have won only 2 Tests outside India(Kingston 2011 & Lords 2014). 15 defeats and 6 draws.