Been awhile since I checked in on this, but there are some interesting points.
(1) LaFortier as the most recent Warden.
I really like this idea as it solves -- at least in my mind -- some nagging issues from Turn Coat. To what's been stated above, let me add one tiny additional assumption. Assume for the sake of argument that the existence and nature of "The Warden" is restricted information known only to the Senior Council members (and maybe not even them). There is some support from Rashid on this.
First, splitting the White Council into factions is simply not the same kind of stakes that earlier and later books establish. While no law requires every Dresden File to have all creation as the stakes, a possible fracturing of the White Council is just not that significant. Sure, the Wizards think that they are super important and that the Senior Council is the most important of all; however, in reality they are just one player in the Great Game and a fairly downscale retail outfit when compared to Heaven, Hell, Winter, Summer and even some of the more scuffed powers like the Fomor, Asgard and Hades.
If the White Council split, would it really matter that much? Harry and McCoy seem to think so, but I doubt that this is really true.
Second, if splitting the White Council is the goal, why not kill the Merlin instead? If you wanna see some infighting and jockeying for power, just wait for that guy to ride the Night-train to the Big Adios. Why not Mai? She seems less capable of defending herself in a physical confrontation than LaFortier. If you can program Lucio to kill La Fortier, you can program her to attack anyone.
Third, Christos has been a disappointment as a Black Council suspect. Harry and McCoy were initially convinced that he was, but in the subsequent years, I haven't seen any real evidence that he's actually bad -- he's just a self-important jackass (like all the others). Indeed, I don't think we have any real evidence that he's actually anti-Harry. Crucially, his injuries (badly burned) likely prevented him from voting on expelling Dresden. (I think only Merlin, Mai and maybe Liberty cast votes).
Given this, just opening a Senior Council seat seems like it doesn't quite fit. On the other hand, given ALL of the subsequent events, clearing a Warden out of Demonreach and then trying very hard to get rid of the "accidental" replacement or suborn him makes sense. It also makes sense that the Senior Council didn't immediately appoint a successor (assuming they can) and didn't check up on the place. They are so self-centered they assumed that the LaFortier Affair was about his Council Seat and not his Night Job. No one but the Senior Council knew that LaFortier was the Warden, after all, at least in their minds.
(2) Harry did not "stumble" on the Job
I don't think Harry accidentally stumbled on to the Job as Warden. He was carefully stage-managed into the job by none other than Uriel. In fact, recall that Harry could not have been the Warden without Soulfire. I'm sure an older, more skilled wizard could have managed without Soulfire, Soulfire was just Harry's cheat code to getting that Job a hundred years too young.
(3) Harry is the Adult, not the Toddler
While I like the toddler with a gun metaphor, in this metaphor Demonreach is the toddler, not Harry. Demonreach is sort of a super-natural Bam-Bam from the Flintstone's cartoon. Harry is the adult, because his threat assessment and response software is more calibrated.
