It's skill if you take a long-term perspective. Which means over many, many hands. In any given tournament (including the WSOP) or playing session, luck predominates, but averaged out over hundreds of tournaments/sessions, that is where skill factors in. If you think about it in terms of a single hand, luck is perhaps 95% of what determines the winner of the hand. Maybe 5% is skill. However, given that luck should even out in the long run, meaning that over time you should be as lucky as often as you are unlucky, then that 5% skill factor is the only thing that matters.
But you also need to consider the rake that the house takes out of pots, or in the case of tournaments, the fee you pay that does not go into the prize pool. So to win at poker, it isn't good enough to just have a skill advantage over the other players. You need to have enough of a skill advantage to overcome both the other players and the rake. Rakeback or bonuses offered by poker sites can help with that, if you play online.