I cannot show any of my thousands of photos in the Finder...
Photos has exactly the same ability to manage photos within a package or referenced as iPhoto has, so you'll need to explain what you mean here
...(and if I try to export them, nothing happens either).
How are you trying?
f I copy any photos from the app into a folder, the created date (critically important info) is changed to represent the date that the photo was copied (!!!) — who cares what date a file was duplicated
Again, just like iPhoto... you're confusing File metadata and Photo Metadata.
There are two kinds of metadata involved when you consider jpeg or other image file.
One is the file data. This is what the Finder shows. This tells you nothing about the contents of the file, just the File itself.
The problem with File metadata is that it can easily change as the file is moved from place to place or exported, e-mailed, uploaded etc.
Photographs have also got both Exif and IPTC metadata. The date and time that your camera snapped the Photograph is recorded in the Exif metadata. Regardless if what the file date says, this is the actual time recorded by the camera.
Photo applications like iPhoto, Aperture, Lightroom, Picasa, Photoshop etc get their date and time from the Exif metadata.
When you export from iPhoto to the Finder new file is created containing your Photo (and its Exif). The File date is - quite accurately - reported as the date of Export.
However, the Photo Date doesn't change.
The problem is that the Finder doesn't work with Exif.
So, your photo has the correct date, and so does the file, but they are different things. To sort on the Photo date you'll need to use a photo app.
and basically everything is a total mess.
So far you've not really explained anything except that you don't understand how photo dating works. So, for help you'll need to describe the issue in a way other people can understand.
I also tried to drag groups of photos into my media management app and nothing would copy over at all.
Both iPhoto and Photos are media management apps, so you're using a third one? Why? Why use two apps to do the same job? That makes no sense. What app is it?
Oh, and you've never noticed Image Capture (in the Applications Folder)?