I think we have a few ‘stuck-in-the-mud’ photographers here, relying heavily on past experience, which is understandable, but not being open-minded enough about what’s possible. In many ways, iOS sucks and is limiting creativity, but not for illustrating and certainly not for photo editing.
I salute you, Neil, for pushing the envelope. Given the depth and creativity of the free-hand artwork being created on iPad, there is no question that serious photo editing can be done on it, especially since we photographers are not starting from a blank canvas like illustrators are, but from a mostly finished image.
I shot my way around SE Asia for 5 weeks last summer and 95% of editing was done on iPad or iPhone. Snapseed worked very well as did TouchRetouch (brilliant, in fact!) and Pixelmator for putting the photos onto a white square background for viewing. They weren’t 100mp Hasselblad files, but the easy and simplicity of editing was there, and that’s what iPad does.
As far as small icons go, an Apple Pencil takes care of that. In fact the Pencil makes edits even easier.
Some are concerned about colour balance, which might be valid for precise technical shots, fashion, food and studio work, but for the vast majority of nature, travel and landscape photography, colour balance is more than accurate enough.
iPad can’t do everything (e.g. printing to my Epson 3880), but it can easily be the future of photo editing, if you’re open to it.