His waiting is soon over.
It is important to understand that Legato doesn't, exactly, want their efforts to fail and to tear Jeneora down entirely on principle. He doesn't believe humans are worthy of mercy, and thinks his god is being led astray, but he also is not so arrogant as to think he is more knowledgeable than God himself. This is a test, not a capitulation. And since it is a test, what it needs is an outside element simulating the effects of humans being terrible. Because they inevitably will be. He is providing a valuable service by simulating this element. What's more, he can assure the safety of the most important things in the world (the plants) while doing it, which is ultimately much safer than leaving it to humans to screw up.
For the plants, anyway. Humans are immaterial, as is their suffering.
The only hiccup in this plan coming to fruition is God himself, but in his experience, God is wise and perfectly amenable to reason. Zazi can deliver unto him a neat treatise, penned by Legato, explaining his logic. It is much safer for the plants if Legato causes mayhem now to stress test Zash's hopeful system. Legato has a vested interest, and will in fact work very hard, to make sure that the plants themselves are entirely unharmed by the chaos that is planned to be unleashed. This is better than random human elements can say. But, for the sake of a fair test of his brother's ability to actually make hard decisions himself, God himself will need to give them room. Because, obviously, if Knives stays in Jeneora, he'll just ultimately solve any problem, and his ability to problem solve is not under question here.