I think space time 5 times means people below level 70 wouldn't be able to do it. That wouldn't be again unfair to people below level 70. And as far I have seen monthly mission is not about fairness, its more about choices.

Maybe they dont expect us to complete all missions. It might be like you have to make a choice esp last week when there was elite instances and plot instances. No one can do both of them unless you use stamina potion which is unnecessary as per me. And probably some missions are for certain groups like ranked battle for jonin medal guys. Just us the above comment mentioned jonin medal guys get very few benefits, and this maybe considered one of this.