For the record, I highly disagree with the notion that there's "almost no" nobles like Mathilde in-setting. Like... certainly, nobility and inherited positions of power have a lot of downsides that are readily noticeable and which we've seen for ourselves (and personally punished), and certainly, I'm not gonna be a cheerleader for it, but like, Mathilde knows several nobles who she knows actually do good things for their subjects, and is even friends with several of them: Anton, Abelhelm when he was alive, Roswita, Boris, Konstantin (the EC of Wissenland), Luitpold and Heidi (she totally counts), Belegar, Thorgrim, Kazador, Queen Marrisith, Cadaeth...
Nobles actually doing things is expected here. And mercifully, the things they're expected to do very often benefit not only themselves but their subjects. Investing wealth into their subjects so they can generate more wealth, like Mathilde did with her fief, is probably not all that uncommon - people like having more passive income.
And we could also talk about how many nobles lead their armies from the front because they often have the benefit of really good martial training since childhood, and good equipment - and we've seen both the benefits and the drawbacks of that, with Abelhelm and Belegar.
...I suppose, if you want to be really cynical, that we could take "nobles being good isn't uncommon" to be the ultimate demonstration of how this is a fantasy setting.