P/60 isn't a bad metric, but I think people drastically overvalue it. It has been demonstrated time and time again that P/60 is often not sustainable as ice time increases. Tons of sheltered middle 6 guys have awesome P/60 and are unable to sustain that when asked to play an extra 3-4 minutes of non-sheltered ice time against quality competition.
Again, it's not a bad metric, but focusing on it without context doesn't tell me much. ROR was asked to do tons and tons of heavy lifting in Buffalo. His zone starts were 41/59 in favor of the defensive zone, which was the 27th most "defensive" zone start rate for NHL players with 800+ minutes at 5 on 5 last year. Only 1 player ahead of him on that list had a P/60 above 2.00 and only 3 of the guys ahead of him on that list finished in the top 100 of P/60.
His job most nights was to shut down the opposing team's top line and Eichel's line was put out there in any favorable offensive situation/matchup unless they had just gotten off the ice. There is certainly room for improvement with his 5 on 5 production, but looking at just P/60 without context makes his season look a hell of a lot worse than it was. He played a role that absolutely tanks P/60 and does so for almost every single player league wide. His 5 on 5 production last year was not good enough even with that context, but his 3 year P/60 is right where I would expect it to be. I don't have many concerns.
Edit: After doing some digging, I found a weird quirk with ROR's stats. NHL.com has him at 34 even strength points while Corsica has him at 24. Moreover, adding his even strength points, PP points and shorthanded points on Corsica gives me a total of 50 points. ROR had 61 points last year, so Corsica's stats for him are brutally off. Excluding 10 of his even strength points would certainly lead to a P/60 well below his 3 year average. Obviously some of those 10 could be 4 on 4 or 3 on 3, but it certainly wouldn't be more than a handful.
