This isn't true. The SDC coins that went into the minting (of Shadow) transaction are visible on the blockchain. When you go from Shadow to SDC, the coins still have a history and that history is visible as well, though obscured by ring signature mixing (and stealth). How effective that is depends on how long the coins where in the Shadow system, the amount of usage of Shadow, etc.

The distribution issues americanpegasus mentions are real. Sill the Shadow system is decent technology, especially if you stick with Shadow-to-Shadow payments and don't convert with SDC, worthy of a mention for sure.

AEON has slightly better theoretical anonymity properties than Monero at the moment, though Monero will have better anonymity properties once its hard fork activates in late March (at the cost of being heavier-weight). Neither is perfect. Nothing is perfect.