If I want to select and copy part of the picture to paste over another part, same thing. Adding text of different sizes and colors, very easy.
The Photos.app and also its predecessor iPhoto are programs to develope a photo and make it look better - improve the colors, the lighting, the contrast, noise reduction, minimal retouching, perspective correction. Make the photo look better, but keep it a natural photo, as taken by a camera. Basically, Photos is correcting, what the camera should have done.
What you are looking for are tools that combine parts of photo to a new photo by graphics composition. For this you need a different kind of program - Photoshop, Pixelmator, Affinity Photos, Graphic Converter, etc. These programs have been designed to combine different layers of graphics to create new photos. But the price to pay is a cluttered user interface with lots of extra tools for Graphics.
When I want to develope a photo I prefer a photo centric user interface with only the tools needed to touch up my photo. It would be graet, if Apple would bring back the editing brushes we had once in iPhoto, even on the iPad to add local adjustments - dodge and burn, blurring, sharpening. I amusing Luminar Noe, when I need local adjustments.
To combine two photos or to add text and other graphics I do not mind to have to switch to a different editing extension.