So true, especially early in any card game decks tend to be VERY similar, no matter how well balanced, because there just aren't many options yet.
However I will say I don't like the "If every deck has copies of the same card in it, that card is probably overpowered." guideline... atleast not if ignore that "probably" cause the "probably" is very important. Over use of cards is certainly a cause for concern and a reason to investigate the power of said cards, but just because a card is used alot doesn't necessarily mean its too strong. All too often in card games people use bandwagon jumping as their primary deck construction technique. One guy wins a major tournament and some of the cards he used get released to the public, your almost assuredly going to see use of those cards jump. The truth might just be that he was a really good player or got lucky but all too many players prefer to go with the proven winners over trying to innovate new winning combinations.
That said, in this case the Japanese team in charge of balance has had 10 sets and several years of experience with this game and all of these first set cards, so if anyone would know which ones are just overly hyped and which ones truly are over powered, they'd be the people.
The bunnies of Lavato have special abilities, like 'Action Skill: Make Carrot Disappear.'