Correct Answer 100 wrote:
They are amazing runners.
That's not the point here. Even a low/moderately talented male could be described as "amazing range" with 2:04/4:33/15:35/32:30 for example. The point here is that some runners would score similarly on the IAAF scoring tables for a large range of events.
On the other hand you got someone like Rudisha who surely can't run anything close to an equivalent 5k/10k to his 800m PR. His range would not be described as good, but he is still an "amazing runner".
Webb was often described as "amazing range", but he admitted that when he was in his 800 PR shape his 10k was lackluster and when he was in godly 10k shape he didn't have the same 800m ability anymore. So in this case, it's just good, quality training for the current events a runner is training for.
If someone has the perfect range at a given time, it's rather a sign that his training is not ideal, because he is not peaking in any even at that time. He just trained himself to be mediocre at all events, without being good at anything. He could have a globally better range by focusing on each event temporarily, PRing, then doing it for a different event.