One feature I really miss in Affinity Photo is the ability to change levels for each channel.
Currently the levels adjustment only allows to change the levels white/black/gamma globally for all channels. Most other image editors allow to switch to the red/green/blue channel and adjust each channel's level individually. This is already possible with the curves in Affinity Photo.
I would also like to see a usability improvement for the way one switches between these channels. Currently (in curves), I have to click onto the drop-down menu, choose a channel, and click again. It would be much easier and faster to just have four buttons on the top of the histogram, one for global curves adjustment, and one for each channel. And finally, if these could be activated by a shortcut, then it would be perfect.
For comparison: In PS there is a drop-down menu, but at least it can be switched quickly with Ctrl+1, Ctrl+2 etc. In Photoline channels can be switched by buttons.
Anyway, most importantly, the levels adjustments should have the ability to edit each channel's level individually. The aforementioned usability improvements would be a great addition.