There are few scenarios where Soil out does Lustrate. On a Warrior after 2.1, Lustrate is going to be an insta-2k heal. Soil will need to modify 20k damage to equal that in terms of pure mitigation. Lustrate is a part of SCH healing, and needs to be managed appropriately. If you are 1. using Aetherflow stacks for Energy Drain, and 2. only using Lustrate as an "oh crap" button, then you are being horribly inefficient with your healing.

Not saying you can't do it that way, since I'm sure I'm about to hear the retort about what content you've healed, but it's far from ideal. Your Caduceus example, also, is a horrible example of how to heal on a SCH. Skip the soil, double Lustrate (around an Adlo if you are that concerned). Cad won't be throwing down enough damage in the next 15 seconds for Soil to outweigh the Lustrate heal.