In the current version of Krita, when one presses the shortcut to increase brush size, it works like this:
1 → 2 → 3 → 4 → 5 → 6 → 7 → 8 → 9 → 10 → 11 → 12…
But I’m not a pixel artist and I never need to distinguish a 5px brush from a 6px one. I’d like it to work, for example, multiple the brush size by 1.5 and round up to the closest integer:
Not as a shortcut. But you can manipulate the number and the value of the steps offered by the Quick Settings Docker if that may be a way for you to work around this missing setting.
To solve this, it would need a feature request. For instance, like that these steps can be adjusted like you can already adjust the zoom steps in Krita under Settings > Configure Krita > General in the tab Tools under Zoom steps between powers of 2. If Krita would offer this for brush sizes too, you should be able to find a good setting for you, and if you create such a feature request you can also ask to maybe implement the choice of the different methods to vary the size of the steps, like power of 2, Fibonacci, logarithmic, or whatever you may think of.