I have a similar frustration, on my Surface Book 2, for some reason the Photos default Windows app is sluggish to death. I have to scour all sorts of third party applications to finally find one that loads correctly. I'm using an extremely vanilla configured Windows too. I rarely open that laptop anymore because of all the bloat. Someday I'll smoosh over Windows and just dump Linux on top of it, even though the support for Linux isn't the greatest.

The Photos app on Mac irritates me too, you cannot just force it to scan everything, it has to "do it in the background" which feels like never.

I've looked at all sorts of alternative photo gallery programs, and it feels like none come close to what I wish Photos was like, without being slugs.