It's never the team with the best support that wins the tournament tho (:
The jungler is obviously a big impact role, that's why players like Canyon or Kanavi are worth so much.
That being said, china doesn't have great junglers either so idfk why is that relevant.
Depends on players whether the impact is higher by a mid or a top. Chovy will always have more impact than Santorin just because of the player. Bin will always have more impact over FBI regardless of the role.
The high impact roles are usually mid and top because that's where the most skilled players usually go to.