I've spent the last couple of years shooting, and a fair amount of cartridges in building up a memory bank of sight pictures (and I'm still adding to it) by shooting a lot of maintained lead on everything apart from a couple of target types.
I can't see how anyone can be consistent to a decent level with just gun speed and not seeing any lead at all, your timing would have to be incredibly accurate on every single shot and surely it's easier to gauge a gap that you have to give a target rather than how fast you have to swing.
Prime example was a mate who up until about this time last week shot everything swing-through then saw a coach who introduced some maintained lead leaving him baffled as to how much lead he could see shooting maintained gap compared to what he saw when coming from behind the target, pushing through, and pulling the trigger.