If you share such infos with us, then tell us what exactly was poor? IPTV is IPTV, streamed content is like it is, the box can not deliver something what is not present. Overall picture quality and improving to get best eye feeling is from user to user very different. Some like in advance options to set SDR and not HDR, others something else and some never discovered that the box have (holding vformat 2 sec.) Display Mode and Imprex Engine to set the picture quality like they want. Standard settings are not always best solution for all and need to be changed if the picture quality doesn`t fit.
I just found the resolution looked lower than the other two devices when comparing the same content. General eye feeling also, as you mention. Mind you I am comparing it to two devices that have better video cards than the Z8. That being said I am quite discerning (picky? <grin>) when it comes to the video. Are those setting you mention actually within the Z8 settings?