You do pay for what you get with Walking Ballista, but the card is a powerful mana sink that has an easier ceiling to realize than Hangarback Walker
Producing board presence via forage is a great payoff for cracking Food and buffing your team is a great payoff for filling the deck with squirrels
Bestow delivers exactly that
You and your opponent have to discard at the same time, so theres a chance youll discard different card types and you get an extra card out of it
Niambi checks a lot of boxes
Kaargra Warfang isn't as bad, but her favor pool mechanics, cards like "Fickle Fans", and a "The heroes cannot win" rider on her flip side mean a dire situation can result in Hero victory, or dominant play from the Heroes can be stalled out into a sudden defeat, with only so much that can be done about it