In fact no. Bigger heavy machines do less damage than smaller ones overall. You have to look at the whole field, not just where the tires touch. Where the tires touch the ground the heavy machine is worse, but the smaller machines touch the ground in a lot more places and so do more damage.

Farmers are now using GPS to ensure all the tires that touch the field drive exactly the same place every pass, every year. Where the tires touch the ground is hardly worth farming, but the rest of the ground is undisturbed and so much healthier.

I would think so. There is a lot going on in this area, see e.g. https://pixelfarmingrobotics.com/robot-one/ and https://www.odd.bot/

There's also the trade-off between width of the worked area and the treaded surface made unusable for the season. If you have any tractor work steps between seeding and harvesting, you want all those runs done in exactly the same tracks to minimize waste.

A "small robots" revolution might still come, on the coat-tails of agrovoltaics: if/when someone in the right position begins thinking the panel scaffolding as dual use, doubling as a "rail network" for robotic tools. I believe this could become a feature of agrovoltaics installations as unremarkable as overhead cranes on factory floors.