I don't know what you mean by "related to the same outcome".

The fact is that while arrow speed and cast are related, the relationship isn't necessarily intuitive, directly proportional or common sensical but based on mechanical physics. The reason is because, as previously noted, arrows of different weights absorb varying amounts of energy from the bow and arrows by their design have considerable drag which will slow down light, initially fast arrows quite dramatically.

I'm sorry if you don't understand this. I don't know how I can make it more clear, but again cast and FPS aren't the same thing and those who presume otherwise are in for a surprise. However, you're at liberty to believe anything you want. Far be it from me to interfere with that.

Have a nice day.