VAUConnFan, I respectfully disagree.
Please correct me if I am wrong, but I think you are using the phrase "offensively challenged" to mean very little scoring. I would say Mutombo was more "limited" in terms of his offensive abilities, in that he was not scoring outside the paint.
For his first 11 seasons in the NBA, he averaged between 11 and 16 points per game in every season except one (and that was 9.1 ppg).
And during those 11 seasons, he averaged at least 11 .5 rebounds per game in ten of them (putting up 10.8 rebounds per game in the 11th).
While his productivity declined in later years, keep in mind that Mutombo entered the league at the age of 25 in 1991. So by the time his 11th season concluded, he was about to turn 36, which is well past the prime for basketball players.
So you see, Mutombo was much, much more than just a shot blocker for his first 11 seasons. He had a long professional career because he was a double digit scorer, a great rebound, and an elite defender, not just someone who "shaped a long professional career around his shot blocking ability."