I wanna guess the criteria to get a Dendro Vision is 'chasing a dream' since both Rana and Collei got them while doing such. Collei 'chases' Amber in 'I want to be helpful like her', thus obtaining a Vision. Rana remembered her old dreams of being a great ranger and thus obtained one.
Still not definite enough though, we haven't heard how Baizhu or Alhaitham got theirs.
