Why do we get these quests if we can't Duel?
To be clear, you can duel via matchmaking, but the population of players are your level bracket and league are probably pretty low so its hard to get matches.
The local duel one is not doable, but should be address in an upcoming patch update. There are several other quests that need to be removed from rotation, like brewing an XP potion.
We will fix this issue before Rifts are implemented.
What are rifts?