The realm shattering punch is cool conceptually (deprived of power it currently might be, it's still the power of a GOD), but using it in the Munchen fight is just a net negative, isn't it? Loss of stats from using it, missing out from absorbing the wisp, which gives a lot of Qi and a permanent 5 Qi reduction to using spells (which may include Dao usages?).
It's always a net negative. If you ever use the punch you're hurting yourself more than anything.
Especially with Muchen, beating him isn't worth it reward wise unless you have Tri-Dao or elemental. It's better to just let the devil take over so you can get all the same rewards plus absorb the wisp... too bad dying to Muchen is completely bugged.