QB K P i can see
RB makes no sense to me

please explain

There are lots of real life examples of guys who run really fast, bench press a lot and have fast 3 cone drill times who don't make it in the NFL. I view athleticism as body control - can you use you coordinate all your movements at high speeds while people are trying to hurt you?

it seems like to me that would be a handy attribute for a RB to have

he gets 8 like a punter

It's just the default value given. I agree it should be more but you can customize your own position roles at D2 and up.

you seem to be suggesting that the defaults may not be ideal

why would someone build a game like that

Because their vision was to have us compete against each other. Thus you have a lot of decisions to make.
Among them how you weight what go's into your perfect (pick a position).(to learn this I would suggest 2 things: Look at the help file that shows you what attributes are important for each position. And second, Look at NC winners teams and see what attributes are grown for each position. Armed with this info you can experiment with your own teams.)
The default gives you suggestions. But if you learn the game you can fine tune the parameters of how you want your perfect(again, pick a position).
Make the right decisions here and with the other choices and in long run you will build a winner.
If you want things pre programmed for you so that you don't have to do a thing then you might as well watch a movie.

ATH = head on a swivel maybe, much like body control

but a kicker doesn't need that at all

like a OL in the run game he just needs to keep his head down and do his job

I still think it's relevant. Like you said should be higher. It's at an 8 as a default setting for us to change how we see fit. If you have two punters both with exact same potential, gpa, attributes and measurables but one has higher ATH I'd argue the higher ATH is a better overall football player. I forget where I read it once but from what I understand after the core attributes are factored, ATH is a modifier. Maybe it'll make a punter avoid a block and get the kick off? Or be in the right position to tackle the returner? Not a core by any stretch but depending on your tendencies and preferences as a coach shouldn't be entirely overlooked. At least in my opinion.

And by, "not a core" I'm specifically talking in regards to a kicker/punter.

I agree with Mdodge. Ath to best of our knowledge is some kind of modifier , the higher the ath the better .
Maybe it has better chance to drop it inside opponents 20 ? Or to get a booming kick off ? I will take the better core numbers but if they are close I will take guy with better ath and GI too.