I was, long ago, a microwave radio tech. It's cool to me that line of sight issues still create issues. For the most part, my old line of work is dead because tech marches on. My immediate reaction is that your neighbor should be able to use a troposcatter shot[1] to fix his issues, but I suppose the provider has bigger fish to fry.

I'm a bit sad about it, because tech advances have technically made this sort of thing dead easy.

[1] https://en.m.wikipedia.org/wiki/Tropospheric_scatter