Problem for Tendulkar was he was captaning a poor team. All the hopes were on him. If he failed and India lost, all the blame would be on him. You can't blame a individual for a team losing.  We don't understand the pressure he under . A billion people expected him to perform and his team knew if he didn't,  they would lose. That is not very easy to deal with. This is why I rate Kohli extremely highly as a captain.  I don't think people understand how difficult it is for him to maintain his performances with the amount of pressure he is under.  
I think if he had a better quality team , he would have done a decent job as captain. 
PP think captaincy is all about tactics. It's not all about tactics.  If a player leads from the front it can raise the performance of the whole team. Most of the great captains led from the front . Also a player will earn captaincy through performing so it will matter even more when you are actually captain

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His legacy is still great, but had he been a successful captain it may have been slightly higher. But not every player is a great captain .