Don't watch IDSF events for technique, the dancers are mostly too young to know what they are doing, though they do put on quite an impressive show. Sadly the same can now be said even for a lot of the professional events. But what the couples who win, often there are subtle but key differences.
For example, many dancers even into professional finals do not understand how to make shape their bodies so that both can occupy the same point in space. Instead, the detour around each other. This detouring means they take a very large step one (since the partner has stepped sideways out of the way) but because they have lost alignment they are now constrained to take a smaller step two. Contrast the true experts, the best of the best current and retired, and you see that they stay in each others way but move together. This creates slightly less travel on the first step, but a much larger free release on the second, which is the way the modern waltz has always been explained.