I had an epiphany an hour ago, so here we go...
Everything comes back to matchups.
Some matchups are based more on luck. Mostly those where 1 deck contains a Hard Counter to a major part of the other. For example, let's take Medicham and Draggytrode. Sure, Medicham has a HUGE advantage in the match, but Draggytrode CAN win, it just needs to get extremely lucky. Since the Draggytrode player can not pull off their usual strategy while Medicham is in play, you must rely on good topdecks and favorable flips to have any hope if winning.
Also, some decks are dependant almost entirelly on luck. Decks like Flariados that rely on a bunch of flips are hoping that the coin flips in their way. Of course, they can get really bad luck, regardless of what opponent they are playing.
Some matchups are more dependant on Skill. These are the ones where each person can get setup and use their powers to their full effect. Queen vs LBS could easily go either way depending on player skill and deck build. Topdecks and luck could play a large roll, but as long as each person can use their Quick Search and other powers each turn, skill will play a very large roll.
So... Everything, and I mean EVERYTHING comes down to matchups. If you get the good matchups you can easily get to the finals of any tournament. But if you get bad matchups, forget it. You're not making the finals.
All the player skill in the worlds will not get Rock-Lock to beat Medicham