The issue seems to be that at deeper levels all digging gets reduced, so the fractions of a meter the auto digs get gets reduced even farther.
Viewing post in STRATA: Dig Through Time comments
This is a great diagnosis - thank you. You're exactly right: the v1.1 soil-hardness mechanic divides dig power by depth resistance, so at deeper strata each auto-dig tool only adds fractions of a meter and the purchases stop feeling meaningful (which is what w8gr was hitting). That's a side-effect of the rebalance I need to undo - hardness should still slow you down without making auto-dig upgrades feel inert. Reworking the curve so buying a tool gives a real, visible m/s increase at any depth. Really appreciate you pinpointing the actual mechanic - that saves me a lot of digging.
v1.2 is live, and it's a direct result of your diagnosis - thank you. You were exactly right that hardness divided everything by depth until the affordable tools added nothing. I kept the early-game hardness (so the v1.1 economy fix stays) but flattened it in the deepest strata, so late-game auto-dig now sits in a steady ~2.5-5 m/s band instead of collapsing toward zero. Upgrades visibly move the needle at any depth again. You're credited in the devlog. Would love your read on whether the deep game feels right now.