Well, lifting weight without any mechanical aid (e.g. a lever of some kind) is the best measurement of strength, but the bench press isn't the right tool. If you wanted to really gauge someone's overall strength, you'd have them deadlift; it utilizes the most muscle groups of any lift and, mechanically speaking, an athlete should be able to deadlift more than they squat or bench. At my best as a powerlifter, my deadlift max was 200+ lb pounds heavier than my bench because bench press only uses a few muscle groups.

If someone wants to accurately describe their character's physical power/strength, they should use "lifting from the ground" as the means of measurement. It's also going to be the most common form of strength used in a fight anyways, because almost all fighting utilizes things like hip drive and the posterior-chain, which are essential to squatting and dead-lifting.

That being said, using bench press as a means of measurement isn't the issue. The issue with that example is that the person who came up with it didn't know enough to realize that benching 300 lb =/= running 60 mph. I bench pressed 405 lb for two reps when I powerlifted, but I don't know anyone alive who can run 60 mph. Bit of a difference. That's what I mean though; lot of systems are vague or just.. not put together particularly well.