Just as food for thought, it could be argued that some of those events you used as evidence that their targets weren't plot devices were themselves plot devices. 
As to the Queens in particular, OW41 says this:
You know, with all of the vagarities that crop up in DFRPG discussion, I find it amusing that there is actually RAW settling the question of the relative degree of plot-deviceness of the Queens. :p
Note also that WoJ states that the White Council (all of them; every wizard on the planet) might have a chance against Mab -- but only outside of Faerie and only if they had her True Name and only if all of her countless Fae minions stood back and watched. So that's pretty darn plot-devicey in my book.
http://www.jimbutcheronline.com/bb/index.php/topic,11012.msg462610.html#msg462610
Adressing this in parts:
Plot devices: by the theory that the PC's should do extraordinary things, they too are plot devices.
My opinion is that the Lady of the lake should be more powerful than a Lady of Summer or Winter. Similar to Leah, weaker than a queen, but very mighty. I don't really think something like that should be statted out unless you intend it to have to fight or unless your PC's have a chance at defeating it.
Mab is cerrtainly stronger than most anything in the Dresdenverse (cannonically speaking).
There will be inconsistencies between novel and game. There has to be really.
In my opinion, anything statted out in the OW is not a plot device power level foe. Your mileage may very well vary.
