Martino led the Catalan giants from July 2013 to May 2014, failing to win any silverware other than the Supercopa de Espana.
And the Argentine says he struggled to cope with the magnitude of the job, which is now held by Luis Enrique.
"These are the feelings one has after 10 months of work and analysing everything," he told AS. "I felt I couldn't improve this fantastic team and I could not happy at reaching one of the best clubs in the world.
"[The current Barca] is a much improved version. They don't create as much as a team but they have a very high level of attackers who can decide a game.
"The team evolves over time and players need replacing."
Martino went on to take the reins with the Argentina national team and is happy with how Lionel Messi and Javier Mascherano are now being utilised by Barcelona, particularly after the former endured a difficult 2014.
"There are two beneficial things happening with Messi and Mascherano," he added. "Leo starts on the right side and Mascherano is being played in midfield. And that's good.
"Before Masche only played at centre-back and came to the national team to play in midfield.
"Messi's been fine in 2015. To determine what happened [in a reported disagreement between Messi and Luis Enrique] without being in the dressing room is difficult.
"He's getting the ball, competing, creating goals, and involved to the benefit of everyone."
