Dear friend. The iMac is NOT a pro machine.
1) Screen: Every frackin screen issue with Apple (yellow imac, retina mbp, ipad) has been due to LG screens. Now all screens on iMac are LG. God only knows what will be wrong with these. Pros can not use these reject screens.
Nearly every professional display in the past 10 years has used an LG IPS panel. Reject screens? Whole runs are made for Apple and technology advancements are made under contract from Apple.The issue is Apple's volume more than anything to do with LG's technology. If Apple only used Samsung's panels you'd still have issues due to the unavoidable failure rates manufacturing has.