Do you think Khamzats physique is big factor to his success?

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He's huge and athletic but typically in MMA you want the least torso possible, and Khamzat has a super long salamander torso

Ideal MMA physiques would include Jones, GSP, Topuria, Volk, Usman, Merab, etc

To the bolded: not when it comes to grappling. For grappling, a longer torso to leg ratio is advantageous due to a lower center of gravity, a longer back for more leverage in grappling the opponent to the ground, and more compact mass due to the larger torso.

For striking though and arguably bjj (due to longer limbs being ideal for submissions), you are correct.