Might sound unexpected at first, but I believe removing this "feature" would allow for a better experience using the Thaumonomicon.
I don't think there is a single page where zooming-out feels beneficial to the player; instead it only highlights lack of content and the repeated background asset. Perhaps implementing this feature to begin with was a bit over-ambitious.

The only time I can think of where I definitely wanted to be able to zoom was viewing the augmentation research page. I'm not sure whether that speaks more to how disorganized the augmentation research got over time or how useful zooming actually is, though.

When you wrote zoom, did you refer to zooming-out? If so then yes, I suggest it isn't useful, and probably the opposite. It seems it was not present in Thaumcraft 4 and was added in Thaumcraft 5, but I don't think any category benefited from it since.

Another idea is to limit the maximum amount of zoom-out, perhaps to 1 extra level, rather than this: