Photo export quality

The quality of JPG images exported from Photos has suddenly turned very poor—they're visibly grainy. I can make them a tiny bit clearer by choosing Maximum quality from the export menu, but they're still not great. (And they used to be fine.) Choosing PNG instead improves the quality, but images are huge (1.2MB at 1000 pixels wide). Is there another setting I'm missing? I've been doing it the same way for 10 years.

(I haven't updated to Catalina yet.)

Attaching JPG, PNG, and a screenshot from Photos. The screenshot is much better.