The first of a series comparing Test captains by their basic skills rather than captaincy.
Data up to May 15, 2021. The ICC XI Test of 2005 is not included.
Most runs (2500 and above):

After all, Graeme Smith has played the most Tests as captain.
Kohli is in 4th position, the best for Indian players as well as current players. Root and SPD Smith are some distance behind, and Gavaskar still further behind.
Most centuries (6 and above):

Graeme Smith again. Kohli is in second place here and will probably overtake him. SPD Smith is next among current players. Gavaskar with 11 is next among Indian players.
Fifty-plus scores (18 and above):

Here is Graeme Smith yet again. Kohli is in 8th position here, which is the highest both for Indian players and current players. Root and Gavaskar are some distance behind.
Highest individual scores (225 and above):

Led by Lara with his world record 400*. Kohli with 254* is the first among Indian players and current players. Williamson (251) and Karunaratne (244) are next among current players. Kohli’s 243 is the second highest for Indian captains.
Highest batting average (Min 20 innings, 50.00):

Bradman’s 101.51 is far ahead of the next, who is SPD Smith with 70.36. Williamson (62.81) and Kohli (58.60) are the next among current captains. Tendulkar and Gavaskar are further down.
Highest strike rates (Min 1000 balls faced, 50.00):

Exact figures for balls faced are lacking for some who played before 2000. However, it should be clear that Kapil Dev would have the highest strike rate.
Shakib Al Hasan has the highest among current players, although he may not captain his side again. Even SPD Smith may come back.
Kohli can be said to have the highest strike rate among undisputed present captains.