Its been a cornerstone of archetypes, such as Gardevoir ex, Lost Box, Raging Bolt-Ogerpon ex, and others
Interestingly, the Sapphire portion of this deck can benefit from the ones from the Sapphire/Ruby deck recently released
And if its later and you want to trade the attacking 3/3 for a nasty creature, knowing that the Champion is likely to be blocked and die, well, that was using it just like a four-mana sorcery that reads, Put a creature from your hand onto the battlefield. And dont forget the potential reusability of the Champions exert later, as well as Greens acceleration getting the Champion out and swinging earlier than its 4th turn sell-by date the other colors 4-drops would normally have
The plan is for The List to change subtly from set to set, bringing in cards that might make sense with the set we're in, but it will mostly stay intact from set to set, meaning you all will get to learn what cards are in The List
Compare that to something like [card]Serra Ascendant[/card], which enters the battlefield as a 6/6 creature with lifelink for just one white mana, and its easy to see why that card is a format staple