People will use the best cards no matter their rarity. They could be the most common cards in the set, doesn't mean they won't be any less prevalent.
As for rare cards having powerful but specific abilities, isn't that how it is already? Verlaat sets it to day time, Eskutia sets it to night time, Catherina has her array of buffs (but is made of paper). These abilities, when you center a deck around them, can be powerful (well, maybe not Verlaat yet), but you can't really just slip them into any deck and expect much; catherina might be the easiest to work with, but again, she's made of paper, so you'd have to tailor your deck at least some to protect her. The other 5-star cards seem (from my casual glancing and lack of gameplay) relatively balanced with other cards of their level, at least as far as in-game stats and abilities are concerned.
on a related note, I highly recommend anyone interested in this topic read the articles When Cards go Bad
and Rare, but Well Done
. They are both by Mark Rosewater, head designer of Magic: the Gathering, and go into detail about some of his (and WotC) philosophy behind balancing cards and rarity. Both articles are from Mark's Making Magic
Column, in which he basically talks about different aspects of the game: how sets/mechanics/changes came to be, insight into the creative process, and so on.