Actually, they are incompatible, as you can only use the Wild Shape Strike in Wildshape and you can only use the Falling Stone Strike in Mountain. By the rules you can't use them both at the same time.
prototype00
You'd get both the benefits and the drawbacks.
Since the stance limits you to one type of Strike, you can only make one type of Strike. Since the stance gives you that Strike, you wouldn't be limited to the Strikes given by the spell.
So yes, you're likely losing out, especially if Gargantuan.
"Why is Godzilla lifting up his limbs like that?"
"I think that's Crane Style."
(Jumping kick to Rodan's head.)
"That really didn't seem to do much."
"No. Nothing really."
On the flip side, you now have a Strike in Pest Form.
You could even be a Crane using Crane Style, albeit non-flying until spell level 4.
I don't think there's a good way to overcome that Weakness, but gosh I want to make a ninja cat or something now. Maybe even rat or teenage turtle.
You could take Assurance (Athletics) and trip many enemies, and I'm thinking your Monk's status bonus to speed would still apply.
Hmm...
Duration's too short for normal use (among its many flaws), but you'll surprise the guard who thinks he's catching a loose animal.