Archmage of Runes has a nice pedigree to see play, and being a 3/6 giant wizard helps, because you have good stats and good creature types
Now there are other things that come into play when playing Magic and winning Magic: a well-constructed deck is going to be a powerhouse regardless, but if your opponent has access to expensive cards that are able to do multiple things when yours can only do one, that makes a difference in how the game will go
Radiant Greninja can currently be found in several decks, like Gardevoir ex, Palkia-Dusknoir, Raging Bolt-Ogerpon ex, and even Lost Zone Box
Giratina isn't cute or cool in the conventional way
Even years after its release, the demand remains sky-high because it contains some of the most high-value hits from the Sword & Shield era, and is an absolute gold mine for anyone who loves Rayquaza or Umbreon