I don't think it's rigged that much
note I said not "that much", not that it's not at all.
I'd have to start collecting data to be sure, but I think I get what I consider to be the best reward (which is rare ninja frag, seal scroll and coupon, exactly which depends on the exact content) at least 70% of the time.
Which might still be below par (6/7 is about 85%) but... certainly not 50/50. Again, i say "might" because I'd have to collect data to be sure.
It would be reasonable to expect the "extra reward" of getting everything and not "missing the good stuff" for being able to clear all breakthrough. But for one thing that's a bit too easy right now, I can do it on auto and never lose a char 95% of the time (I can complete it w/o losing a char 100% of the time if I don't auto)
And.... even if they do let us get all of the prize pool, they could just make the pool worse which effectively does the same thing.
So really, there is no winning this battle, regardless of whether they make the change you want, because you don't know what else they might have done.