You won’t find a better external monitor, maybe the LG 5K but that costs nearly as much as the iMac. There are simply no external monitors at this pixel density, with this colour accuracy and brightness, except for the LG 5K.These iMacs are kinda worthless. May as well get a mini and a better monitor. 629 for mini.
Once you factor in a keyboard, mouse, monitor, webcam, speakers the price will be similar to the iMac.