Personaly, I like Explore too and I like building more unique builds, so that made my choice easier
Spell Pierce also works well when your aggressive deck wants to get in for damage early and defend your creatures against Red and Black removal
The initial fear of Stoneforge Mystic homogenizing the format, making any deck whether tempo, midrange or control a Stoneforge Mystic deck has not come true, and the Kor Artificier rather looks for specific deck building in which it naturally slides in than being an auto include in anything which can splash white
In the 99 Not much to add
(Im delighted to have this debate in much more detail, if you find this crass or flippant.) Again, as Ive said for years , I cannot think of any plausible reason why TPCi does not sell the artwork for these cards as prints on its stores
Commander is a particularly popular variant of this