It's potion time!
...Charizard is much bigger, and the tale was about David - the small guy - triumphing over Goliath. Plus, Silvally got shot down first than its 2 other teammates, and all Lycanroc forms are smaller than 10-year olds.You could ask the same about Gladion's Lycanroc and Sivally. The bigger they are, the harder they fall.
It's a tradition David and Goliath story.