Elon is working on replicating it now with “X”. He’s already said he wanted something like that for the US

That was always my assumption about why it happened, but it turns out that’s not the case at all: https://youtu.be/CUjt36SD3h8

In aggregate, yes, but any individual wave of light is still traveling at c. You get the appearance of a slower wave because secondary waves are generated that cancel the original one in such a way that it makes a combined wave that appears to be slower.

To be pedantic, photons never accelerate. They only ever travel at one speed in one direction