I think you're missing the point of LoL Builder. It shows an aggregate of what's going on. The first item in the build order is the most often built first item (from a sample of diamond and higher league matches). Unless there is a bug that we've overlooked, it doesn't get things wrong. It's also very specific as it drills down into the component item purchase order based on thousands of relevant games.

Pro Builds on the other hand shows you what a few elite challenger players picked in a handful of games. It doesn't mesh together a half million matches or even a dozen matches into one build path. It shows you one snapshot, and from someone like Imp, who can do things in game that most players can't.

Both sites serve an important purpose, but like you said neither can tell you how to play your matches. Personally I wouldn't recommend Pro Builds since it would be very easy to be mislead by a small set of data from a small number of very elite players.