Seems like cheating. The expansion of the universe is a correlation between distance to things and their red shift. You still need to have a proper measure of the distance to something rather than using it's velocity as a stand-in for distance. Particularly if you're looking at things like flow fields.
It's not. It's honesty, and keeping the measurements in the form that will remain more usable. What we measure directly is the redshift. The estimation of the distance (that is, the exact value of the H0, the Hubble constant) is done using various methods and the results aren't bad, just not precise enough to use it combined with the redshift. That's what makes us preferring the redshift now, as the speed can be exactly calculated from it: https://en.wikipedia.org/wiki/Redshift
Knowing that the Universe is "flat" ( https://en.wikipedia.org/wiki/Shape_of_the_universe )
allows us also to do good calculations, even if we still don't have the exact value of H0. In fact, it's also not so bad: the estimates based on the Planck satellite, measuring the state of the Universe 13.7 billion years ago as the galaxies and stars haven't existed, and the ones based on the Hubble satellite data (measuring the state of the Universe much more recently) mismatch only some 9%. It is amazing enough for me. This difference, after more research, can produce some new physics discoveries or make us improve some engineering (and we surely should invest in more research) but it's quite good for everybody else: even if the "emptiness" from this article affecting the Milky Way is not 700 million but 730 million or 670 million light years, it won't affect our plans: for example, the Andromeda galaxy is just some 2.5 million light years from us and we estimate it will collide with the Milky Way in some 4 billion years, give or take. Should we care much if the "emptiness" is 268 or 292 times farther than the Andromeda is at this moment?
See my other response here for the way you can calculate the distance from the speed, based on your preferred estimate of the H0, it's simple, just less precise at the moment than simply stating the speed (or the redshift).
