A few hot-fix changes are coming to Hearthstone's Arena mode
In Patch 10.4 the Hearthstone team introduced some big changes to the way players draft cards in the Arena mode, but some of the changes didn't go exactly as planned.
Before the patch, players drafted cards that were of similar rarity. After the change, cards are now aligned based on strength of the card as opposed to their rarity, meaning you can have options for Rare cards alongside Epic cards in one of your selections. As a result of this change, players have been noticing a drastic strength in decks they come across in Arena.
In this hot-fix, the chance to draft a Legendary card will be much lower while the chance of selecting a weaker card will be higher. Jesse Hill, a Community Manager, talked about these changes in a forum post. "We agree with the concern that many of you have expressed that there are slightly too many high powered cards appearing in Arena decks."
The changes should tune down the power in both your opponents and your deck whenever you go for an Arena run. You should see fewer Legendaries and you won't have an incredibly over-powered deck with multiple Legendaries, but neither will your opponent.