How is boost pivot grabbing a myth? It's a real technique and is a very good technique to know how to do. Especialy on Marth and MK because they both have up specials that get in the way of the normal straight walking chain grab. Also flashy.
Well, this is my thought after having done frame advance testing with Falco.
If you attempt a regular dash grab vs a dash attack canceled grab (boost grab), the difference is very minimal. It's not a significant boost when you compare pivot grab to boost pivot grab. So, I thought Falco might not have a boost grab that is actually of any different length and I tried looking for it in frame advance.
A boost grab would like like this:
Frame 0: Shove control stick
Frame 1: Dash starts. Input dsmash to make a dash attack come out.
Frame 2: Dash Attack starts. Input grab command.
Frame 3: Go into dash grab animation.
....
Frame 13: Can catch opponent with grab.
A regular dash grab can be done more quickly.
Frame 0: Shove control stick
Frame 1: Dash starts. Input grab.
Frame 2: Go into grab animation
....
Frame 12: Can catch opponent with grab.
When I compared these actions with each other, the boost grab did go a bit noticeably further. However, I when I delayed the regular dash grab by one more extra frame to match the boost grab action, the distances between the two looked extremely identical.
So, in short, I think dash attack canceling isn't even needed at all. The real "boost" in the dash grab comes from how many frames you delay between starting a dash and doing a grab. Performing a dash attack cancel grab mostly is useful for timing if anything, but doesn't actually give you a boost I believe.