Language is a very poor substitute for freely flowing electrical information - it is evolved to compensate for the bottlenecks to external communication - bottlenecks that are lacking an internal analogue.
It's also a highly advanced feature - something as heavily optiimised as evolved life would not allow something as vital as cognition to be hampered by a lack of means for high fidelity external expression.
But the most fundamental boon that it offered was in terms of planning and organisation. Before language we'd point and grunt and go there and do the thing that we were gesturing that we were going to do.
But that's a very crude form of planning - you're pretty much just going all in on Leeroy Jenkins.
But actually (and horrifically) I think it's the gift of Kane that speaking and planning permitted; well organised humans (the smartest things on the planet) have been figuring out increasingly better ways to both kill each other and not to die themselves in a brutal feedback loop for a very long time now.
It's brutal as fuck, but it's Darwinian gold.