That's where detailed range notes come into play.
Every draw to fire (no matter how many followup shots) is trackable when you're use a timer.
Detailed notes will also give you data on your 2, 3, 4, 5, however many shot strings including times to first shot and splits.
I fact I'd say a data set that includes notes with various strings from 1-6 gives you more to go on than just a set with draw 2's and Bill Drills.
Draw 2's tend to turn into a test of finger speed ("double taps" so to speak) not necessarily true sight tracking. Bill Drills often turn into rhythm shooting instead of sight tracking and grip stability.
Varying the number of shots while still tracking it with a timer gives you a picture of what you do all the time.
Of course visual cue starts can't be tracked, but IMO practicing to react to a visual cue is worth doing. Even if you can't quantify performance gains you can definitely qualify them after you've done it enough (much like playing the "hand slap game", you may not know exactly how much faster your reaction is but you do know you're not getting slapped as much).