Oh, thank you thank you thank you for developing this plugin!
I had serious issues with my photos being displayed all soft when I use them in my blog at wordpress.com.

Solution:
– Install “JPG Image Quality” plugin (yes, it hasn’t been in active development for 3 years now, but it apparently works just fine even with WordPress 5.2)
– Install “Regenerate Thumbnails”
– Use “WP Admin” to access the admin menu (not usually shown on WordPress.com)
– In Settings – Media: Set the image quality to 100% (or slightly lower, though you start being able to discern the difference at about 96% or so).
– In Jetpack – Settings – Performance: DISABLE the Site Accelerator! (yes! the site accelerator caches the images on WordPress’ central server, and as long as that happens any image quality you set on your own server will be totally irrelevant)
– In Tools – Regenerate Thumbnails: specify all thumbnails to be regenerated.

I am sorry to see the Site Accelerator go. But … I really cannot live with the (lack of) photo quality it enforces.