A lot of this game comes down to level and party development. Much is scaled to your party, though area is a factor. What may be "high end" along the Arnika road may be "low end" somewhere else.
Generally, you can figure that the farther away you go from town, the more difficult an area will be. But that is not always the case. Many have trouble at the mines with Tanto wasps (LOTS of them). If you go at a low level, say 8/9, the monsters will be much easier, and no Tanto wasps will be around.
Still, I wouldn't recommend the mountain wilderness for a low level party
If you find yourself being outclassed by everything you meet, then you're in an area you're not ready for. Back off, level up a bit, and try again later. The game is open enough that you needn't follow any one route specifically.
Nightowl2