Yes, and you don't 1-shot things when you are leveling. You 1-shot things when you're max level going back to leveling zones.
To get a bit challanged can be fun for some people.
Explain to me where the challenge is going back to leveling zones and doing the quests you didn't do while leveling, but with the quests + quest mobs being the same level as you.
Taking 5 more seconds to kill something you would otherwise kill in a 1-shot is challenging?