Unlike what you would expect, small robots do more damage to the soil not less. Damage to soil is not linear with mass, A massive robot will do twice as much damage where it touches the ground (wheel tracks most likely, but there are other choices), but it will touch 10 times less ground to do the same work so the total averaged over all the land is much better.

For the same reason, tracks generally end up doing more damage than wheels: you get somewhat less damage while going through the row, but they touch/damage far more ground when turning and that adds up.