Crimped wires break next to the crimp where they were squeezed on smaller sized wires. I've had this happen several times in my old cars. I can see crimping on 10 -12 gauge and larger wiring as not being a problem, but for the smaller stuff soldiering and heat shrinking is by far superior. If I'm using a form of connector I lightly crimp the spade or bullet connector to the wire and then finish them off by soldiering them as well.
If your wires are breaking at the crimp, the connectors are not of a good quality or not the correct size for the wire. A good quality connector supports the wire by the insulation on the wire that is next to the exposed wire/crimp. I currently own a 63 year old airplane with crimped connectors from the factory and have not had any wiring failures at the crimps. I have, however had wiring failures when the cloth insulation on the original wiring cracked and the wire underneath failed from work hardening due to vibration.