Its helpful for all team members to be, as you put it, "competent and fast", its not absolutely necessary (in order for Scrum to work), and in a lot of companies, its not the case.

The purpose of Scrum is to highlight issues and bottlenecks in the 'system' so they can be addressed.

"Wide skill variances in team members skillsets" is one such problem, and a fairly common one. One remedy is to drop the dead weight, either through management/hr action or natural attrition. Another remedy is to upgrade the skills of the people who are "behind" using the people who are "ahead" as mentors.

- The Consulting Company

>"Scrum requires that ..."

Interesting trait of scrum - whenever there is scrum related discussion the no true Scotsman fallacies immediately pop up. By the way, scrum is actually a methodology to get something out of non-delivering teams. For everybody else it is just like throwing sand into their engine's cylinders.