Absolutely right, and despite what Roblev and crossref have been saying, the support runner
does not have to stay in, or maintain some fixed, relative position to the ball carrier to always be in a position to receive a non-forward pass or offload, or to go into a tackle through the gate. All he needs to do is be in that position
AT THE TIME THE PASS, OFFLOAD OR TACKLE IS MADE, and it only takes a single check step for a player who is running beside his ball carrier to achieve that.
A support runner in the situation shown in the video might just slow down and cross behind his ball carrier if he thinks, anticipates (or if his ball carrier has indicated) that he is about to cut infield, so that he can receive ans outside pass or offload.
Spot on, again, and the other thing to consider, of course, is materiality. Have a look at the direction the would be tackler was running in the first few frames of this clip...
He was initially running in a direction that would have taken him in front of the support runner. IMO, had he continued running in that direction, there may have been a small possibility that he could catch and stop the ball carrier, or at least try to put him into touch. That chance evaporated (along with any materiality that might apply if you thought the support runner was obstructing) when he
chose to change his running line to push/charge into the support runner. Again despite what Roblev will have you believe, it is clear and obvious that the player steps off his left foot and changes direction towards the support runner. This is the
only C&O infringement - 10.4 (e) - in this play, and one in which there would have been a very good case for a PT and YC had he succeeded in pushing the support runner to plant the ball carrier into touch.