Well, I find the amount of rocks OK. And the quarry should be almost undrivable. This is Snowrunner so there should and must be really difficult roads and places that are almost impossible to reach.
I have played the game 100% through and now I play the second time from the very beginning but using only the worst basic trucks and scouts. And I have managed to enter level 21 so far. The places that were so difficult in the beginnig feel the second time easy even with simple basic truck if you only use time and plan before hand the route etc.
The second time I first opened all maps and found all upgrades. And in order to do that I made the nesessary tasks to open major routes and opened Alaska and Taymyr garages.
And I do not use engine upgrades because fuel consumtion is the critical point when playing alone. Only upgrades that are needed and are good are tyres and winch. Engine upgrades just increase fuel consumption. And you can manage all tasks with basic engine.