Does it really show him using it? If not I dont think it's really fair to give him it. Like when they say pandas can heal, is it a trait they inherit or a technique passed down?
As far as I know, he is not using it in KFP3, but 1) Po can learn from his opponent and given the connection between panda and chi, I don't think Po cannot learn it. 2) Po may use it in other media 3) Even in KFM 3, when he became the Dragon Warrior, it seems that the previous wound is healed. (he is beaten by Kai earlier)
"One day, during an ambush, Oogway was badly wounded and Kai carried him for days, searching for help. They then happened upon a secret
village of pandas, who used their knowledge of
chi to heal Oogway." (From Kai's page in KFM Wiki)
For Iron Fist's Kun Lun nuke feat, I heard that he absorbed the energy first. If it is right, then IF's output is less than Country level+ since absorption does not only increase himself but decrease the nuke's enegry.
For the mentor feat for scaling to Po, I do believe that 1) that prehistoric mentor may not enough to wipe out people while "everyone is kung fu fighting" even when they let the real life prehistoric mentor fall since KFP people are stronger than dinosaurs which are at most wall level.
The last question is that: do Po have any impressive speed feats? (at least faster than current vs battles wiki profiles version) I have a feeling that we haven't digged the feats as deep as Lupin III.