Bradley being the new "friend on the force" seems plausible. Considering one of the more memorable scenes in Battle Grounds involves him coming to the aid of his daughter. If Bradley ends up becoming a Knight. It will probably be during the BAT since the sword of Love (or Family) is the most likely one for him to wield and it has been strongly suggested that a new wielder for that Sword is not going to happen until then.

If their is a big throwdown between Harry and Marcone, I suspect it will be in the BAT, more specifically in Hells Bells, since that seems like the most likely place for a a resolution against a Hell Knight.

Harry said that if Mab forced him (I.E. Geas like why Fix and Lilly could not choose to help Dresden directly) to follow an order he would follow her order but would be maliciously compliant requiring her direct supervision at all times and become practically useless to her.

Which is not quite the same as convincing her to make a binding promise not to give orders of that nature.

I am guessing that the way Titania bound Lilly and Fix works a lot like the Winter Law Voice thing Molly used on the Driver. Presumably it is the sort of thing that has to be  intentional and protection from that sort of thing is effectively what Dresden received with his mediocre knight threat.

What Mab says to Dresden in Battle Grounds has the option of being ignored by Dreaden, hence the "... you would be wise to follow" part of her statement.

Either she is not trying to magically bind him for some reason (could be respect of Dresden or honoring her implied agreement to not order him to raise his hand against those he loved) or she can not bind him to her will in this case (either she knows any binding will not survive her death or she actually can not because the forces that control Fae interactions recognized Dresden Terms for being her Knight as spirtually binding). Although it is possible their is something else going on there that I do not have enough pieces to put together.

However I do not think Mab broke her word to Dresden with the commentary about Killing Molly Carpenter. However I do think she may have damaged some of the feelings of actual loyalty and trust that he seems to be developing, although considering she is almost certainly aware of the possibility of damaging his respect for her with that exchange it does suggest something about how bad she thinks it could get if Molly became the Queen.