When they were first put on a pedestal, the pieces of Power were simply nine of the most sought after and essential rare cards of Magic s first set
For instance, if its 0.3% instead, that puts it in the 1 in 1500 range, which is more likely
Situationally asymmetrical sweepers are always interesting and almost always very balanced, so the card is likely to do limited good to the coming standard format without harming it in any way
Uncommons are a bit more complicated since the planeswalkers might have slightly different rarity, but 20 of the 80 uncommons are planeswalkers
Aerie Worshippers Attempted Murder Crow Storm Fable of Wolf and Owl Falcon, Winged Wonder Hermes, Overseer of Elpis Knightfisher Mu Yanling, Sky Dancer Murmuration Murmuring Mystic Ominous Roost Ordered Migration Pride of the Clouds Radagast, Wizard of Wilds Ravenform Restless Anchorage Riku of Many Paths Song of Erendil Strix Serenade Swan Song The Raven's Warning
The exceptions are when the UR version of a certain card happens to have a specific feature that the SAR version doesnt havesuch as the aforementioned Ns Zoroark ex cardor when for whatever reason, the SAR card just doesnt land with the community