I too have mentioned this in the past, especially when using the Pencil to move the sliders. It can be tricky to make the movement for the ‘gear down’ action.
My issue is that with some of the sliders, the Colour (Color!) ones for Saturation and Vibrancy in particular, can be too aggressive. I find that they have a lot of unused movement, as for most images I’m ending up with a less than 0.1 increment is needed. It can be fiddly to get into the ideal levels.
I don’t think the size of the sliders needs adjusting though, they’re fine for size. How about a different approach to the two step gearing applied (Photos increases the level with the Option key, and there’s also an prefs panel option in Pixelmator to change the scaling on the sliders – but these are the opposite to Raw Power, and perhaps make more sense for normal use). Certainly on the iPad version, the scales could be the opposite way round.
Just some thoughts there.