Citadel Focus basically treats the relocation of the spiders, the deployment of Johann against Clan Mors, and Mathilde working with Johann to poke Clan Mors as one whole synergistic set of actions, where both Magisters run interference against the Skaven of the under-citadel to prevent any chance of Clan Mors interfering with the relocation of the We to the under-citadel. I apologize, but I think you are straw-manning the argument for Citadel focus, which assumes that Mathilde both prioritizes the successful relocation of the We while following up on her scouting of Clan Mors last turn, and her long run concerns about Skaven activity. Of course, you are free to contest that these three motivations of what "Mathilde" wants to do is OOC, but you need to make that case.
Also, I think that some Plan Citadel advocates want to establish a working relationship between Johann and Mathilde, rather than Johann and Mathilde playing a game of cat and mouse and parallel efforts, with regards to coordinating their investigations of the Skaven, so there's also the motivation to bring up precedence here.