The mid route moves were a big part of the timing issue with Dak throwing to Gallup.
In the play below Gallup is delayed more than Dak expected which resulted in the ball being thrown long.
When watching the All-22 Dak starts his throwing motion earlier in that route than it than it would seem from just watching this view.
When both are in camera view it's fairly straight forward to see where the WR would be with about half as much delay. With zero delay the ball would have been short.
Obviously if the stutter step delay is needed to get open that's not a problem but the WR has to do it with consistent timing such that the QB knows where to "aim".
The QB needs repetitions with each WR on each of these long routes; however, the WRs also need to work independently of the starting QB on perfecting the consistency of their timing.