I love Affinity Designer, I'm using it allot, for UI design for presentations, it's a great tool . I even use it for small texture work when I need to do something sharp . But Affinity Photo it's well how to put this ... I would like to use it but I'm always returning to Photoshop .
Well because the workflow for copy / pasting textures into channels is not that intuitive ( the spare channel flow ... ) and the problem of exporting TGA's .
I prefer a tga instead png's because of the dedicated alpha channel .