There's no debate as to whether they have functional strength or not as their activity isn't based on strength -- it's based on technique and skill.
Here's a short list of what they can do:
-- landing in ways to absorb or transfer the force of large jumps (TECHNIQUE)
-- acrobatics (SKILL)
-- balance a handstand (SKILL)
-- hang sideways from a pole in a flag (TECHNIQUE)
There's a base level of strength that is necessary in any athletic activity. This is all they possess.
It is impressive, but not from a physical perspective. What is impressive is the "mental strength" for overcoming fear, etc.