<snip>Since the Gatekeeper is way more powerful and knowledgeable when it comes to time travel, he sends the player (and his allies) back to the point where the disturbance took place, in order for them to make things right. <snip>
So, Lucas Priest, Finn Delaney, and Andre de la Croix as Dresden File RPG characters? (See Simon Hawke's Time Wars.)
I don't think that's so much inherent to divinations in general as it is likely another instance of Harry being powerful but sloppy. I rather suspect that it would, in fact, have been a Compel for Harry's character based on his 'magical style' aspect. Other practitioners likely would have executed an equivalent spell substantially differently, and at least some of them would manage to avoid that particular issue.
Since the stated purpose of any focus is to improve precision and fine control, I would think that a focus as impressive as Little Chicago would drastically decrease Harry's sloppiness. This is yet again an indication of Cowl's fundamental might and ability.
Further explaining my Heisenberg comment: If the act of observation does indeed affect the observed, we end up with your standard time travel nightmare. Were the changes always intended to happen or did you actually impact the time flow? For a beautiful example of this Ouroborous, I refer you to Marvel Comics "The Starbrand."
As far as using divination vs. conjuration and the 6th law, a non-problem solution to this would be the ectoplasmic reconstructions from the Sookie Stackhouse books where the caster creates an ectoplasmic "ghost" of the entire event, limited to the locus where cast.
I again thank you for an intriguing thread and dredging up some fond memories.