Yeah, I don't think anyone is arguing that taking a spot up 3 isn't a higher percentage shot.
The question is whether, a person's 3-pt ability staying constant, being a better ball handler means he's overall a more effective 3-pt shooter (including the added volume from being able to create his own shot).
I think whoever said spd is irrelevant is just wrong. Even for a catch-and-shoot guy, the faster you get open the more open you will be. Maybe that would be more accurately reflected in a "quickness" rating, but spd is all we have.