If you're not enjoying the content and having fun, don't force yourself to do it.

There's other ways to level your classes. And if you are so focused on getting a secific achievement reward, but aren't having fun reaching that achievement - maybe try something else that's more fun to you?
The game has plenty of options of things for anyone to do. And if nothing seems fun, maybe time for a break or another game?

Achieving something based on luck / RNG is nothing new in games. For some people that makes it more exciting for them. Thinking of rare loot drops in old RPG's, or shinies in pokemon (or rare encounter legendaries). Something being rare or hard to get makes it more rewarding once you finally get it, if you are willing to keep trying. But nobody forces you to keep trying. If you're not having a good time, stop making yourself having that not-good time.