This is how a pro uses FL studio
High quality video of the actual song
I don't know what VSTi's he was using.
Gate To Heaven (Dreameye Mix) is not technically pro, but still incredible, and was made using FL Studio 7 with Absynth 3.4, Z3ta+, Vanguard, and Atmosphere plus the Techno Trance Essentials sample pack.
Break Free 2 is a track by TranceCrafter that was made in FL Studio 10 using Sylenth1, EastWest Hollywood Strings, and EastWest Quantum Leap Complete Composer's Collection. He also used Ozone 4 to master the track after it was rendered to wav from FL Studio.
FL Studio is built primarily for software based composition, whereas many professionals tend to prefer analog synths using DAWs that are better geared towards complex live recording sessions. A lot of people simply don't like FL Studio's workflow. However, there is nothing about FL Studio that inherently makes it less capable of producing quality tracks. A DAW is a DAW. FL Studio can render a song with just as much clarity as any other DAW, a fact that has been proven time and time again (there was a thread I can't find linking to a study proving this at some point).