Everything needs context. Comparing point totals without considering role makes no sense. That doesn’t mean taking into account the PP isn’t important, but it also means that someone who scores more solely due to the PP might not be better.
In general I think 5v5 play is more important, because, as a lot of people mentioned, it is the majority game state and it isn’t necessitated on refs calling penalties. One thing that doesn’t get considered enough is that there’s also far more minutes and roles to go around, which means it’s less likely someone’s talent will be redundant. If you have two great PP half-wall passers who aren’t great shooters, one of them is either going to be playing a less optimal position or playing less minutes on the second unit. If you have two great 5v5 line drivers, they can both get top minutes on separate lines. Role, system and linemates also effect 5v5 scoring, and we should consider those things when ranking 5v5 players, but I think it’s generally less pronounced.
That doesn’t mean the PP isn’t important. Most teams still need strong special teams to win. The difference is that the PP is a lot more structured and points are a lot more dependent on role. Elite PP players like McDavid, Draisaitl, Kucherov, etc all bring a lot of value, because you can design schemes around their talents, but I think there’s lots of guys who are the 3rd and 4th option who score a lot due to how good the PP is and many could be replaced by an average top 6 player and it wouldn’t significantly affect their team’s PP%. I also think there’s some players who get decent PP points because they’re just their team’s best option, but wouldn’t touch the puck as much on a better PP, and other players who play roles like a net front presence who might be a big part of the effectiveness but not score as much.
In general, I tend to put players in three PP categories. They’re either elite difference makers, poor PP players, or somewhere in the mushy middle. For players like Draisaitl, his PP prowess puts him above some players who might be better 5v5. Meanwhile for a players like prime Brendan Gallagher or Viktor Arvidsson, I think their poor PP play hurt them in comparisons against players who weren’t as efficient 5v5 but could perform on a top PP unit. For more mushy middle players, I think if they’re both elite 5v5 I’d rather have the slightly better 5v5 player, because I’d rather have someone be as elite as possible at what they’re good at and then try to improve the PP another way. If they’re both similar mushy middle 5v5 to their PP play, then maybe whoever has the bigger advantage whether that’s on the PP or at 5v5. It’s all about trying to make the best team and maximizing your strengths in every area, which also means certain players are better fits on different teams as well, which is why direct comparisons can sometimes be pointless.