Yes, it's certainly possible that Riker and Worf are mathematically gifted. But if you had a choice to go to either Data or Riker and Worf for math assistance, whom would you choose? It'd be like me choosing an $8 calculator to try and do complex equations rather than seeking help from various websites, etc. Data doesn't know everything, but it seems impossible to me that he wouldn't understand calculus. If there are people living today who are experts in calculus, I don't know how Data couldn't be. Especially since calculus is still very much revelant in the 24th century.