if you don't reward players for level-syncing themselves in the dungeon, other that SP, there will be no point in doing that and people won't waste their time doing that even for a challenge. We want a challenge but what is a challenge if you are not rewarded for it in any form. People like to beat challenging fights but it's null if there is no one knows that, if everyone has the same rewards regardless if they go the easy way or the challenging way, no one will force challenge things since no one will know they went and succeeded.

I might not express it in the most eloquent way, english is not my primary language, but I'm sure you get what I mean.