Rift challenges difficulty should stay at tome 2 level.
Because "in one trial" are holding on complete luck to get bad opponents.
Problem is time/reward will suck huge [Bad word] later on. You will have to invest twice the effort and(or) luck just to get 3-5 fragments. Which is super wrong.
Comments
The only real solution is to make the master challenges completely optional and stick them on their own track. So instead of the fancy map layout you have four lines of objectives.
Survivor
Killer
Survivor Master
Killer Master
This would stop the crazy situation of having a master or killer only challenge blocking the track.
Making Master Challneges optional and not roadblocks to completing the tome would be better