You're not the first :)
If you know how to do masking with video in Davinci, then it all just applies to photos too. I tried today some basic Magic Mask and color tab editing with photos, and it works exactly the same (without the annoying waiting time on huge videos for Magic Mask, ofc).
I've just now had a look at a couple of YouTube tutorials on Magic Mask for video and I think I understand where I got lost. It looks like the tools I was looking for are on the Color tab, and I first need to drag my images in to the timeline at the bottom of the screen and then jump to the Color tab to work with them.
All the tools are here for a good photo editing product - they just need to be extracted and arranged in a way that is intuitive for photo editing, and this would be a legitimate LR alternative.
edit: This is a great video on the Photo tools: https://www.youtube.com/watch?v=HuKgfytA0lg. I do feel a little more confident that I could use Resolve for editing after watching this.