It is only the remaining 5% that are really trained! And rangers are among this 5% so why waste all that training by putting the guy in the front lines? Send hiom into the field to sneak qaround, gather intelligence and get that info back safe!
So Rangers are NOT front line troops. Yes, they can fight and fight very well, BUT that isn't their main job. Their job is to be silent and avoid battle whenever possible.
So why wear plate?
A ranger, when tye needed to be armored, would wear soemthing that allowed alot of freedom, didn't weigh them down and would allow for maximum mobility.
This is my maile set. I ran a leather thong around the neck-line to aid in finding the neck and to add strength, the coif weighs as much as the entire byrnie and the helmet is a light-weight one I made though I have the frame for a better helmet on the workbench awaiting time to cut and form the steel plates.
I'll probably shorten the sleeves and attach them to some vambraces someday.