At the moment, even if you max out this stance (2 points in stance, 3 in mountain palms) you throw out less DPS than without the stance on.
Mountain palms were probably changed by Troj, in the hyuuga revamp topic it says:
Mountain palms does 20/30/40% attack power down from 100% but always procs.
However the passive in game is:
You perform mountain crusher instead of a normal critical when you critically hit with melee or final strike of 128/64 palms strike. Only in effect while Precise Striking is active. Decreases total attack speed by 40%. (3/3)
For reference, Prec strike is:
Learns the ability Precise Striking. When this is active you deal 20% less damage and critical rate increases by 10%. You can't use rapid palms while this is active. (2/2)
Now I don't know if Troj decided to change it last minute while coding, lost the original code in the code corruption, forgot to do it, etc, etc but at the moment the passive nerfs you. The only reason I went into depth here is because most of the time people who see suggestions that has to do anything with math chime in and make stupid assumptions that make my suggestions look foolish.
I tested my DPS on boars, with prec strike on it reduces my attack speed from 275% to 165% (40% reduction), I do not use mountain palms on every hit, only when I crit. It takes 8 seconds on avereage.
Without prec strike it takes 5 seconds on average to kill them.