It wasn't "just" PDO, they've had very bad injury luck this year so far, and the additions they've made have made up for who they lost, but having neither of their 100pt C's healthy at the same time has hurt the Canucks, as well as losing Hronek, Joshua, and Boeser while Demko has yet to make his season debut, Silovs has also really struggled as the backup.
Their early high PDO was affected by several huge blowouts in the first few weeks of the season while not having many big losses. An 8-1 win, 5-0 win, 10-1 win all in the first 10 games.
Through 23 games, the Canucks are 13-7-3, last season through 23 games they were 15-7-1. They've earned 2 less points compared to last year.
As for "legitimate contender," most people said they weren't one last season, and many predicted they would lose to a red hot Nashville, and then get blown out by the Oilers. In my opinion, they're basically where they were last year before the Zadorov trade, a hungry young team with two 100pt C's, a top 2 defenseman in the league and a Vezina nominated goalie that needs to add a top 4 defenseman to be taken seriously. We still haven't seen this team fully healthy.