The idea of the T50 was to have a set of well designed decks that change every week. For a little while T50 decks have been the highest level in elements (months ago).
Players however decided to use it to create "farm decks" and distribute the rare cards as much as possible. I do understand the intent of being helpful and generous, but at the same time this practice actually eliminated "rare" cards from elements.
I know most players sound frustrated when cards are rare, they want them and they ask everyone how to get those, ending up writing in the forum about "how impossible" is to have a certain card (does not happen anymore, it did a few months ago). But I do believe all the frustration is worth the moment when you finally get a rare card that almost nobody else have... also called "wow effect".
Right now winning a rare card is mostly a "finally, was waiting for it" then a "wow". I am aware of that and I intend to change it. I knew about this problem and I have been working on a solution for a while (even before this post appeared)
I soon will be adding new cards that have a new (higher) level of rarity and cannot be a reward from T50 decks. The new water alchemy card (Nymph's tears) is probably going to be one of those and it will replace the "arctic octopus" as the water rare card; the octopus is going to be for sale at the bazaar.
I am still thinking for a name for those cards: maybe "legendary".
Winning a legendary card is going to be purely luck-based, they will randomly appear in the slots, even for lvl1, in very rare occasions, something like a "jackpot". It has to be luck-based because I want it to be unexpected, not something you "farm", it has to have a "wow-effect" and only a very few players will have those cards. Legendary cards do not add new game mechanics that would be available to a few elected, they will make common game mechanics available in a different way.
If a card is extremely rare, a predefined deck configuration (find deck on the forum, buy cards, farm rares, done) is not possible and a more varied deck population is possible.