From reading this thread, it seems pretty clear that it's the Indian members doing most of the "worrying" on behalf of the Pakistanis.
Well let's find out, right?
Influence doesn't mean a loss of sovereignty though.
Sovereignty is a nation/state having authority over and within its own territory.
China has never challenged Pakistan's authority within their own territory, never. If we need some help we'll ask, and since we are friends they will often try to help us.
China is certainly not a saint (or anywhere close), but we are not taking Pakistan's sovereignty, and we are not challenging their authority over their own territory.
Oh we're not worrying. However we would rather that China invested that $20B in India. You could say we're 50% jealous, 50% happy for Pakistan.
Influence in core sectors does equal to a loss of sovereignty. If China wanted, it could cause chaos in Pakistan by just flipping a switch. (not literally of course but you get the idea)
No sovereign country allows foreign control over national resources like that. India welcomes Chinese investment in roads, minority holdings in infrastructure etc