> Isn't that drastically underselling potentially one of the harder parts of this whole endeavor?

Everything in space is hard; but these are Alphabet researchers not NASA researchers, and honestly even the NASA papers I've been skimming through have a lot of simplifying assumptions in them, so that's not something to hold against them here.

They are just saying when they think it's worth considering, after all, not giving a detailed all-aspect proposal for how to make one.