Marksmen are the opposite of their description in-game

Marksmen is the title of the class because the characters themselves are the marksmen in most cases. You don't have to be. You're controlling someone who knows how to land every shot, every time.

That's why champions like Ashe and Caitlin, who are supposed to be amazing shots, don't require you to fire skillshots as their main form of damage.

Compare that to Ezreal, who intentionally does not study magic and doesn't like to be in the League at all. He has the power, but you have to direct it towards a target. Or Lucian, who may be a great shot but is using pistols where others are using longer-range weapons.