riverpebble while it is on paper, its not the same in practice.
Blow for blow, if you just kill timbers and grotes for sure you would get more BBs.
But we are talking about the map as a whole. You get SIGNIFICANTLY more zelus, shadows, raw zeny on niff2, which in turn, you can convert to more BBs.
1.07 vs 1.21% are both low enough that by killing thousands of mobs per BBG, through the nature of RNG, both will yield you the same amount of BBs. So droprates are completely irrelevant in actuality.
For pure BB gain, 5runs of niff2 for me(around 2-4people in map), i get 28 32 35 22 and 19. 5 runs of mjolnir underground (only me in the map, but theres a time when i saw another person there but didnt see him again), i get 31 24 35 20 and 22. Just a small sample and is not really indicative of anything. But the droprate is very low that even if 17% more, doesnt actually amount to much.
Which is why people look at the map as a whole as a deciding factor. By selling everything to the npc, i get around 15-20m raw zeny on niff2, more shadowdecons and more zelus (which can be easily sold to get more BBs)
While in mjolnir, you get like 5m raw zeny and lesser zelus and shadowdecons on top of actually being more difficult to farm as mobs hurt more.
Im not even suggesting to buff mjolnir to be better than niff2. I dont mind it being a lesser alternative to niff2 if niff2 is crowded. But not with this discrepancy though.
A little more zelus shadowdecons drops + maybe raw zeny of 12-15m per bbg is enough to make it attractive as an alternative to niff2.
Right now its a waste of time farming in mjolnir as both niff2 and mjolnir serves the same purpose. Unless youre hunting for the card or mvp