Luck obviously is a factor in the game, though certainly not the only one. Assume you and your opponent are of equal skill level, and both make the correct plays at the correct times, by the book. You are then reduced to the luck of the draw. It really is as simple as that. That, by definition, can be the only deciding factor.
Now, in the real world no 2 players are of equal skill level. And, no one player plays perfectly every hand. Those factors tend, for some, to minimize the role of luck.
I can guarantee that the best players in the world would all admit that when they have won major tournaments, there certainly was a major element of luck involved.