Earlier quoted context omitted.
From my experience I've found that scrumm holds back good, fast developers because they focus on only doing their share in a sprint, when they could rocket ahead and be pounding on the backlog. How can you keep your best developers motivated and busy in an agile/scrumm environment?
That's not a Scrum issue, it's shitty project management. If the scope of a sprint is so far out of whack that fast developers are running out of work, then you're misestimating the complexity of deliverables. That sort of thing gets cleared up pretty quickly if it's being managed correctly.
What i see is not that work runs out, but the best developers on the team throttles their effort lower, so as not todo too much extra work.