Go outside and let me know if your vision focus is 100% of the light your eye receives. Then, when you walk around, let me know if you can count every leaf on the ground as you're walking through the woods looking straight ahead.
We're talking about entire people here though, not specific leaves. People who are wearing a lot of equipment and are actively moving, both of which create sound and draw the eye's attention. These two scenarios aren't really comparable. I challenge you to go outside and, while looking straight ahead, not notice a person who walks ~10-20 feet in front of you.
If you were to dive into sound, I'd argue that elves should be able to hear up to a mile away given proper noise ambiance. I'd also argue that you'd be able to discern much more from noises, like direction of movement, enemy numbers, and possibly equipment types. My next argument would be that the original dark vision visual should be reinstated in the case where senses are properly calculated, only expanded to characters with stronger senses than others (not exclusive to darkvision). The result would be specific races being MUCH more capable than other races based simply on the fact that humans might as well be deaf and blind when compared to an elf. At what point do you draw the line?
Don't let the perfect be the enemy of the good. The system can be improved upon without necessarily making it 100% accurate.
