Backgammon and Chinese chess (or Chaturanga etc) should not be used to decide World Chess Championship...
Why not?
A triathlon is a real thing. (I didn't invent it). Running, swimming, biking.
There are separate World Championships in all these sports. The cycling world champion is not decided by triathlon, so why should chess?
Here's my suggestion.
Let's play with the old Chaturanga rules.
1. Queen (Vizier) moves 1 square diagonally.
2. Bishop (Elephant) moves 2 squares diagonally.
3. No pawn promotion.
They already exist in Chinese chess!