Just a little comment, precision machines have been hand flattened and tuned for years with you guessed it scrapers. Even this day in age, certain machines must be tuned and flattened by scrapping only as there are currently no machine big enough to grind them along with the fact that the grinding is not as accurate as the scrapping. We are talking about tolerances that far exceed what we require for skiing.
Currently tuning equipment allows the non skilled users to do a good job, IE. select program and push button, if all is working correctly you've got a good tune.
The top tuners still tune by hand and learning how to do this should be part of every advanced skiers skill set.
My only fault with the video was that he laid the scrapper on its edge and flexed it while scrapping. This actually will cut a convex into the base. The 4mm scrapper should reduce this as we all tend flex and lay the scrapper over to speeding things up.
I have used various files to flatten bases in the past and yes it does require practice and there is an art to it. Most times now though I will have the base ground flat (less time and effort) and do the rest myself.
As to base structure since I'm not worried about times. I am less picky here and usually have a universal cut done at the time of flattening.