So, adventure loot still need to be adjusted, but BB devs are way lost to make it happen. Though it wouldn't be that hard to "get the framework right"..
Start with..
- Introduce a new non-tradeable adventure currency, eg Skulls, usable to increase drop chance of special loot.
- Let every adventure have a "special loot slot" containing either something "special" (a buff, building or follow-up adventure) or some (amount depending on adventure difficulty) Skulls.
That way a rubbish drop chance" doesn't have to be that rubbish every time (but I don't think it should be possible to gain a 100% special drop chance this way - more likely 30%-ish at most).
Let's say every drop chance boost would have a Skull cost equally to adventure difficulty and, to get maximum boost, needed to be spent that many times equally to adventure difficulty.
That would ATM (still need some tweakings) make..
VLT having a Skull drop of 8, a drop chance boost cost at 8 Skulls per tier and a total cost at 64 Skulls (8 Skulls x 8 tiers);
..while..
WotS would get a Skull drop of 3, a drop chance boost cost at 3 Skulls per tier and a total cost at 9 Skulls (3 Skulls x 3 tiers).