Any dev who can write Java can write Objective-C, and there would be real benefit in switching.

> for all but a handful of companies like Google and Facebook

I think this is a mischaracterization. A lot of companies need something at Java's strength or above on the backend. It is a common problem. And organizations with those needs will account for the majority of web traffic.

> heavy number crunching

Also a mischaracterization. Even simple tasks become computationally challenging when you're doing them for a large audience.