[quote=@ColourlessKing]
I mean Ran exists for one. And that guy fights as the main guy. 
[/quote]

Ran is both a Fisherman and a Spear Bearer, however. I don't know which was his first position, but he fills both roles as does Novick; usually it's Novick as the Scout and Ran as the Fisherman but if they need to they switch to Novick being the Fisherman and Ran being the Spear Bearer.

Again, positions aren't set roles; they only matter in team fights and only apply to what roles you are currently filling. If someone was capable of filling multiple roles then they would probably fill whatever gap needed to be filled, such as Ran filling in for a Spear Bearer because a team needs one even if it's not his best position. Generally the Fisherman is the strongest position because their role on the team is to be the one that does the fighting, with the other positions supporting that. That doesn't always mean the Fisherman on the team is the strongest member, but it does mean that it's the position with the strongest members on average.