A strikers training is very different to that of a wingers or even a Forward.
A striker is drilled to take accurate shots more, when to make runs in the box, headers etc etc.
A strikers job is to concentrate on "Inside the box" craft, a Forward or a Winger is not.
Sanchez is a Wide player, whether you play him as a Forward or as an out an out winger is down to the formation.
Usually a high level winger will cover both areas hence why they look WC compared to bog standard wingers, Ronaldo, Messi ect have too much talent to just hug the touchline.
Just because a Winger is good enough to effectively be / act / contribute like a 2nd striker doesn't mean they are in fact a striker.
Sanchez isn't even a CF (Bergkamp, Del Peirro role) he is def a Wide player, just because you cut in or can shoot a ball does not make you a striker.
Giroud, Lacazette are our only true box strikers, Welbeck is sort of half / half, ST come Forward, mainly because he's not good enough to be a striker so he gets used as a Forward because he's mobile.
Podolski is a Forward.