Why skilled Jett player can't produce top tier performance with Raze and vice-versa?
Because they are different subclasses.
Raze is a space maker. The point of raze is to make space. Blast packs cover a lot of area, boombot to check if space is clear, and nade to clear space.
Jett is a escape agent. You can make risky plays and get away with it due to her abilities. Dash and updraft let you get away, smokes provide cover.
The two are very different and require different playstyles.