I think the tools are good but definitely take some getting used to. I've struggled myself but actually by now, genuinely come to like them.
First thing I think is to get a 3D view. Change angle, bring your view down low and actually work out what you've got to start with because it;s easy to miss. Pena for instance is on a really quite extreme hill and Muertes isn't exactly flat either. A birds' eye view won't cut it, look at it from other angles. I'd also clear all trees first, can replant them later and (think about) re-laying existing paths, which definitely helps in tight spots. On my machine the space bar toggles between straight and curving paths (as well as fences obviously)
An organic looking park (rather than a square, regimented one) is less frustration for a first go (which is counter intuitive) and adding access paths up to buildings (rather than letting path guide the building placement ) helps paths stay flat. You can sometimes (but not always) rescue a path that has a slope across it from a building added second, by using raise on the other side but definitely use the smooth tool first (as well as after). Smooth tool helps .. a lot.
Lastly I think you have to be patient with the tool because the land tends to "flow" rather than cause an immediate big bang effect. You can sometimes notice this as land outside the circle is moving too, the tool merging what you're doing inside it with the hill next door. The game is obviously working this out as you go - so the tool seems slow - but if you don't see anything happening, trying looking a different angle again, and most of all .. take your time with it. if you're going for a perfect park, don't be afraid to demolosh a building before it finishes construction even, and look again at the topology if the building seemed to land wrong the first time.