IMO crimps are often the best (other than brazing/soldering) connections that can be made. I work for a company that carries out as lot of heavy cable work. The sacbles are often under a lot of tension when installed, especiall in moptor terminal boxes ect. We crimp lugs onto these cables, and ivenever had a crimp that was the right size come loose. I have had lugs thaa have been stamped wrong, but thats the point of pull testing all connections.
On smaller crimps, they are absolutely fine too, if you have a decent crimper. Mine cost over £50 but ive never had a crimp fail. Even using 0.5mm conductors on a red crimp, it wouldnt pull off.
If the wrong crimpers are used, or the wrong crimps, then your asking for trouble.