If we're just talking about breaking stuff open (their offensive utility)
Infernape
- gap -
gyarados lucario dragonite are all about the same
- gap -
metagross
When we include stuff like ability to revenge kill infernape and lucario (oh and dragonite if you're running ES now that i think about it) rise a bit. Then the others rise when we consider the defensive resistances they can bring to a team. I think at the end of the day the list ends up being something like Ape as the clear best and then the other 4 are all pretty close. The reason i say this is at the start of the match if I have my full squad i probably have pretty decent answers to the other 4, but when ape comes out it's goddamn terrifying when you don't know what set it is, because it can easily do anything and if you predict wrong without knowing the set you're just dead (and the lack of needing to set up). You can argue something similar for dragonite but at least its main STAB moves (draco / outrage) have notable drawbacks that ape doesn't really have. The SR weakness isn't insignificant either.
I think Infernape is a clear A+ because it can run any kind of offensive set, but I'm not sure if there's gap between it and Gyarados/Lucario overall.
Gyarados lives on its typing and Intimidate to maximize the times it can switch in on stuff. While the old Dragon Dance does run into problems, it still is a pretty decent threat that had always warranted something to check it (a faster scarf mon). It becomes even deadlier if it decides to go bulky to get more DDs. Also, the RestTalk set is still insanely good, Stealth Rock or not.
What's your thoughts further into Infernape vs Lucario? The biggest difference is obviously the speed, which would be a big reason Ape might be more dangerous (in addition to a million coverage and boosting moves). However, Lucario has a much easier time finding Pokemon to switch in on because of its typing (Infernape doesn't like even resisted hits sometimes). And Band/Scarf Tyranitar is a free Swords Dance, that's a huge issue for any team.