While rarity often indicates the broad utility of a card, it also comes with a higher mana cost and doesn't necessarily combo well with the rest of your deck
In these decks that have a lot of very-low-investment artifact generation, Oko can function as a supercharged, cheaper Gideon, Ally of Zendikar that gains loyalty to make 3/3s every turn, except the 3/3s can attack right away (because youre using the ability on artifacts that were already on the battlefield) and the Oko gains loyalty and costs less mana
I also avoided making too many changes because, at a certain point, it would be unhelpful to buy the Temur Rage deck if most of the cards were swapped out
They're wildly overpowered, making them among the strongest "Yu-Gi-Oh!" monsters around, but there has to be a weakest of the three, and that's Slifer the Sky Dragon, the one Yugi gets early on in the Battle City storyline