I disagree. Creating a 2-cost legendary that doesn't take over the game on turn 2 but has the power to take it if left unchecked is greay card design. Double mint is just that. Sure it doesn't shine ad much when you only play 1 in your deck, but play 3-4 of them with the right support cards and it will win you games single-handedly.
Bananasaurus is one of the best mid-range plant in the game. Combo it with other cards that draw you cards to buff it for better value. Example:
Turn 4- Bananasaurus, turn 5- Bean Counter.
Or
Turn 5 Bananasaurus + Big Chill
Or
Turn 4 Bananasaurus placed in a lane where you know your block meter will get triggered first, you keep to power it gives you in your hand to buff the Saurus.
Plenty of wait to maximize those legendaries. Sure they *seem* weaker then Cornucopia or Zombot 9000, but they cost a whole lot less to play too!
