Hi,
i speak as a new player who never played the first chapter of splatoon and only started during the past weekend.
I feel like the tutorial could be more explainatory but people don't really like reading, and i think the devs did their best at trying to teach player to keep their aim up in a learn by doing approach. It's not a coincidence (imho) that all the targets are flying baloons and not ground targets, they wan't you to get used, from the start, to aim stright or even a bit upper then just stright forward.
My feelings: i have an FPS background on PC, and getting used to the controls is very very very hard to me, especially because i'm not that young anymore and probably my brain takes a little longer to get used to new stuff, but aiming "down" or not really stright forward, yes.. it happened to me in the beginning and from time to time it still happens... not literally "at my foot" but not that stright.
To me, this is a consequence of switching from a first person view to a third person one. The character in front of me, my character itself.. i feel like it's obstructing my field of view, and inconsciously i try to move the camera to get a sort of "isometric-ish" view to try to get a more clear view of the surrounding.. This obviously affects my aiming because the crossair (if it can be even called a crossair) is affected directly by the camera.
I'm sure i'll get used to it, now i'm slowly getting the grasp of it and my aiming is improving, little by little.
Harder for me will be getting used to the motion control, with which i feel very confortable for the Y axis, but not really for the horizontal. Hopefully time will be my friend and i'll get used to it too, will try to tweak the sensitivity.
Coming from more then 15 years of playing with mouse and keyboard has its impact.
sorry for such a long reply, I hope it will help veterans understand the feeling of a n00b more in depth :)
Ah, obviously, any advice that can help me improving is really welcome.