Doesn’t compress smaller sizes well

First of all it doesn’t look maintained. Last update 10 month ago, not tested with last 3 major WP releases…. Secondly, the plugin optimises the original image well, but all smaller sizes (defined by add_image_size ) look pretty bad and it seems the quality settings of subsampling and compression are not applied here. No matter what i change in the settings: the ‘large’ size looks the same and even the file-size is almost the same, maybe differs some few kb between ‘lossless’ (looks pretty lossy) and ‘automatic’.

WP 4.9.4