It's faster, but a big reason apple silicon is ahead is because the memory is co-packaged on an MCM. This is the direction things are going.
I meant the following: https://en.wikipedia.org/wiki/CAMM_(memory_module)
That's a way to have the memory close, but still being able to change it (without e.g. hot air station or something).
The real reason however is that going up SoC SKUs at apple gives you more memory channels. Those bandwidth increases you see in specs are because of that, not because the memory is soldered.