I think there are a couple of things to note :
When you are looking at NZ results and suggesting that Muscles Yankee for example has only one horse of note, you are missing horses exported to Australia, including another top class trotter in Skyvalley. Besides Twist and Twirl, Artsplace has sired in NZ horses like Strike Up The Band $204k, Flles Like Magic $169k, Sir Artsplace $166k, Jacka Twain $161k.
When evaluating the performance of Artsplace and his 154 NZ bred foals, keep in mind that they are racing against large crops of foals by Christian Cullen, Bettors Delight, Mach Three and Art Major. Don't underestimate how good these stallions are. These horses are world class with BD, MT and AM currently 1st, 4th and 6th in the current season all aged standings. Note also, it is a long time since Artsplace dominated the northern hemisphere breeding scene.