True. But on a large and very steep hillside - "2/3rd of an acre, but most of it is a 45 degree hill" - it can be extremely difficult to replace the plants holding onto the soil, without experiencing horrible erosion during the transition.
Yep. Depending on the property layout, and how close that slope is to the house, it might be something to contract out and have hardscaping and drainage done.
My last house didn't have anywhere near as much land, but there was a fairly steep hill on the back of the house. We ended up having part of the slope dug out and a "seat-height" retaining wall installed, with drainage installed as part of the build, and lots of low-maintenance plantings. Reduced the work from weekly mowing on a slope to occasional weeding and trimming. But, it wasn't cheap to do properly.
Soil erosion.