Even if you lose mana after activating Sinkhole , if you set up these powerful mana accelerants you can ensure that you will have mana to spend even after sacrificing Sinkhole
Each of these will trigger landfall effects individually, so if you hit three lands, that's three landfall triggers
As an uninkable card, Baloo sitting in your hand with only four willpower and 6 cost makes him a pretty sad sight if you don't have the ink to play him, and even when you do, there are far better options, such as Maui Half-Shark, the all-around better card for the same cost
In this environment, Voltron seems to have been an ideal safety valve ensuring that games did in fact end
Since this card can technically ramp you repetitively, it may be better than it looks, especially in Landfall decks