For those that are questioning why Faulk is on the PK, it's probably because he's been one of the best PKers on the team thus far this year.
Yes, you heard me. He's been one of the BEST PENALTY KILLERS this year on the team. For any player with more than 50 minutes on the PK this year, he has the lowest xGA/60, resulting in the 4th lowest actual goals against/60 on the team. His high-danger corsi against/60 is 3rd lowest on the team, and actual high-danger goals against is 2nd lowest. Oh, and this is from having the 6th lowest on-ice save percentage while on the ice, meaning he's not being bailed out by his goalie. Granted, these numbers are for those who have played more than 50 minutes of PK time thus far, but I would say that anyone on this list could be considered a "regular PKer".
Have I been disappointed in Faulk? Yes. I loved him in Carolina and liked the potential he brought. He hasn't lived up to what he can do, or what he's shown he can do from years past. He's been a darn good player for his entire career and this year happens to be his worst to date offensively. It could either be a sign for things to come, but I'm confident it's an outlier.
But if there is one thing that he should not be condemned for, it's his contributions to the PK. There is very little or absolutely no data suggesting he's been poor there. In fact, he has more of reason to be on the PK than almost any defenseman the Blues have. Want to find the culprits behind the the PK's struggles? Start with O'Reilly, who has been downright bad while on the kill. There are plenty of complaints that can be made about Faulk this year. But him being a bad PKer, this year, is a complete myth.
Player Season Totals - Natural Stat Trick
(If my query filters didn't make it through the copy/paste, just input "penalty kill" for the strengths tab and put "50" for the TOI.)