The 200-card core of Planar Cube contains plenty of great ways to maximize your mana and answer your opponents' threats but few ways to win the game
That card you choose to gift might end up as a harmless card anyway
For example, a Siege card like Invasion of Llorwyn will be exiled and can be cast by the controller without paying its mana cost, even if another player defeated the battle for them
This is a beater in decks filled with token production or Treasure production, and giving it evasion gives you wins
At the very least, your commander is most likely a legendary creature, so that will help with the legendary triggers, but its also pretty easy to fill out your 99 with a bunch of legendary creatures these days
Memory Jar has also fallen quite far from grace, now typically only being used when it can be abused with Goblin Welder and the new Daretti