I've finally given up on Mac's Photos app. I ended up moving all the images that had been in the iCloud Photos app back into Aperture. At some point, I suppose Aperture will stop working with Apple's latest Mac OS releases; but for now it works well enough.
When Photos was announced, what appealed to me was the possibility of having a single, consolidated image library accessible on all my "devices." It never really worked that way, and it wasn't practical with the tools Apple gave me to manage a large library.
If you have a large library, iOS doesn't give you any meaningful way to search for images beyond the date and perhaps the location if the image is geo-tagged. Ideally, iOS would allow you to search all exif data. Even the Mac version of Photos doesn't give you full access to exif data. So, while I could theoretically access my full image library on my iPad Pro, I couldn't do a great deal of useful work on it in the Photos app.
The iCloud library was always struggling to stay in sync. Sometimes it was thousands of images out of sync. This would happen when I'd upload a large number of images from a significant event. I think I uploaded over 2,000 images in October when the Blue Angels performed here. Photos is in no way equipped to handle that kind of load. I'd never ultimately keep that many images, but Photos doesn't give you any real tools to make the kinds of comparisons between images that helps you decide which ones to keep. For a certain number of images, the vast majority, it's relatively simple to use the large thumbnail view to go through and delete the clinkers. But when I got to a couple of images shot in sequence where the composition is mostly identical, I'd like to closely examine both images and see which one was sharper. In Aperture, I can have two images open at 100% at the same time. In Photos, you can't have two images open at the same time, and you can't even maintain the 100% zoom while scrolling through images. If it at least offered a fixed zoom while scrolling, you could flip back and forth with arrow keys and quickly determine which image was superior. But you can't. If you're at 100% on an image and hit the arrow key to view the next image, it loads scaled to fit the size of the window, and you have to hit Z to zoom to 100% and it's impossible to rely on persistence of vision to determine differences in sharpness.
The library also got confused. I'd have duplicate images, sometimes three or four of them, with bizarre file names. These images were full-sized, so they all counted against the storage limit. And I was never certain how iCloud was handling RAW images. It seemed to suggest that with RAW+jpeg images, it uploaded both of them, but all you would ever see was the jpeg unless you chose to create a new jpeg from RAW. In Aperture you have a number of options regarding how you wish to handle RAW files in the library, and it was very clear once you'd made your choices.
For now, I think the best idea is maintain my image libraries in local storage and use cloud services for backup or sharing, not as a primary repository. Aperture remains a superior image management application, with enough editing tools for the majority of my needs. Photos is a significant regression, even from iPhoto, in my opinion. At best, it seems designed to support the very casual photographer who relies mostly on the iPhone as their primary camera. For anyone else, certainly for me anyway, Photos remains an utter disappointment.