I remember seeing that complaint in the past, however, so far I have not seen anything unusual, just a slightly sharper picture.
I only use CoreELEC to play back locally stored SDR videos from my USB HDD. I don’t know if that makes a difference as far as the cartoon effect is concerned.
I did search and find this post:- Odroid N2 test builds - Single Board Computers / Odroid N2/N2Plus/C4 - CoreELEC Forums
I see nothing like this on my setup, images are very natural. If my pictures looked like this, I would definitely disable it. A reply to that post mentions a variable /sys/module/amvideo/parameters/sr0_sr1_refresh and setting this to 0. Mine is currently set to 1 and I have not altered it from the default CE setting.