Both Obama and Mugabe are great Black men who have done great things for their people. It is somewhat unfair to compare them.
Although both started out as educators, It must be understood that Mugabe is a Leader turn politician whilst Obama is a Politician.
Some key difference is that whilst Obama sees himself as President of All the people equally, Mugabe sees himself as president of the Black Zimbabweans(ZANU-pf) first. As a result Obama work may seem weak Too little too late or diluted whilst Mugabe efforts will often be seen as over the top or malicious over kill.
I hold them both in high esteem