Strange Routing 1 is obvious:
There is maxspeed=30 on the main road, and no speed limit on the residential.
So probably missing or false data in OSM. To change this you would need local knowledge.
Strange Route 2.:
There is a speed limit of 90 on the main road, and again no speed limit on the side road. 
BTW:
Seems to be related to
Stick to Mainroads in Villages
Problem mit Micro-Umleitungen im Ort
Manfred