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I started a new Quest and set the difficulty to medium, but all the available opponents under Duels are marked Easy.

Also, I had set the poole to sanctioned: standard, but the opponent I played in a Duel had a non-standard (LEG) deck.

Are these bugs?

Nope. The quest mode difficulty determines the rate at which you level and your opponents become more difficult. The pool determines what cards are available to you. Your opponents' decks have already been made and are not subject to this limitation.