The position of South African ambassador to the United States is the most prestigious and top diplomatic post in South Africa. The position was first held in March 1949, following the upgrade of South Africa's diplomatic mission to an embassy. The post has been held by many important politicians and is currently held by M. J. Mahlangu.
M. J. Mahlangu, the South African ambassador to the United States, is an important politician.
I believe that this is neither correct nor incorrect as, per the statement, while he holds the position of South African ambassador, the statement only says that the role has been held by many important politicians, not that every holder of the position has been important.  Importance is subjective.