The story is a little more complicated than this.
As the video suggests, if you use only upper arm / shoulder tracking, the edge picking amount is more similar on all strings. That part is true. However, the rest is not. For the most consistent tone, you want less edge picking on the lower strings, which is exactly what happens naturally if you use some amount of wrist or elbow tracking in your technique.
You can test this very easily. Grab a fresh pick from the bag, something smooth like celluloid or Ultex. Test 45 degrees edge picking on the top string. Now test 45 degrees edge picking on the low string — way scratchier. The only way to reduce that is to use less edge picking on the low string. Wrist/elbow tracking motions do this automatically.
Note that these tracking motions also change the spot on the string where you are playing: closer to the bridge on the top string, closer to the neck on the low string, all other factors being equal. But paradoxically, if consistent tone is what you are looking for, this effect is a good thing. Why? Closer to bridge = brighter, closer to neck = darker. But more edge picking = darker, less edge picking = brighter. These two effects cancel each other out. Again, you can easily test this.
To further complicate things, note that as picks wear, they become more scratchy on the top string, and less scratchy on the wound strings — often significantly less scratchy. In other words, the scratchyness tends to equalize across the strings. This is most noticeable with materials that wear, like celluloid, tortex, and nylon, where the difference can be pretty dramatic:
If you only play worn picks, the amount of scratchyness will be more similar across all strings, even if you don’t change your edge picking.
Personally, since I like even feel, I prefer a worn pick with the flat spot already dialed in, so all the strings feel as similar as possible. The small amount of scratch this introduces on the high strings doesn’t bother me, and it is pretty small — I demonstrate what this sounds like earlier in the same video. Moreover, since the slight scratchyness is present on all strings, I prefer it.
Finally, note that some players like a very scratchy feel on the wound strings. Teemu Mäntysaari talks about this in our interview, how Wintersun uses a fresh Ultex pick when recording for the most scratchyness they can get on rhythm parts. So the creative choice is up to you!