That's not really true? We do subtle just fine, see all the stuff we were doing when we were Van Hal's Intrigue adviser; we did plenty of sneaky about without really anyone else being the wiser, we kidnapped a guy form his own home. Maybe we're not always the most subtle, 'handing toppling one domino to see the others fall perfectly' agent out there but we're not exactly incapable, it's just that for the last however many turns we've been in a situation where that isn't really possible. First as part of the expedition, where we needed results fast rather than results quietly and since then as Belegars Learning Advisor where most of our job is figuring stuff out but we occasionally moonlight as a scout/assassin. And critically most of our targets are those that we can't really do subtle with, skaven and orcs are both pretty hard to infiltrate for us requiring the use of magic, even then it's imperfect and not entirely reliable, and they don't respond the same way humans do to psychological levers.
Honestly, unless we turn our attention towards internal Empire shenanigans I don't see much opportunity to stretch our more subtle skills. Until and unless we go to Nagarythe.
Ehh, I'd agree that our time with Van Hal was more subtle, but that's not the same as subtle. I was going to agree on the Stolpe op, but then I went back and reread that part, and it's totally Mathilde. She walks in, and mindholes everybody she comes across. Repeatedly. She throws Stolpe off a balcony and into a shit wagon while distracting people with a griffon scream. The final end result is subtle, sort off, but I hesitate to give her that many subtle points for it.
And let's consider the spy mistress stuff. Did we recruit agents in the dark of night, in hidden back rooms and in-cognito? No, we rode up to them wearing our wizard hat, on our magic horse, with our large sword, and asked them to tell us stuff. Pretty much all of her work turns out like that.
Also note, I'm not saying Mathilde isn't effective. She really gets things done, but in most cases she's fairly blatant about that. In the words of a minor knight house: She might be unseen, but people will be feeling her.
Really, the more I think about it, the more I believe that Mathilde just doesn't want to be a shadowy figure of mysterious actions. There's probably an english essay in there, psycho-analyzing her actions in the context of her fear of rejection and being overlooked instilled by her childhood as one of a multitude of peasant children, and then the reaction of her family to her magic. (Her fear of mirrors and overcoming it would be super juicy. Lot's of good essay in that.)
Also, something I couldn't fit into the last post, but really wanted to: The first title she got, Dämmerlichtreiter, was for blatantly doing magic all over the place.