"Crimping a connection is far easier for most people to do,"
And perhaps not, since most newbs will go down to the auto parts store and buy a $5-with-500-pieces crimp set that looks just like the $50 set but is doomed to fail. In crimping, just as with soldering, folks need to be aware of the details. The cheap sets are often just dimensioned wrong, and the cheap sleeves made incorrectly. They'll get you home, they just won't last ten years. Or they'll fall apart a good percent of the time.
Acid-core solder is a good suspect for a failed connection. Or maybe wires that weren't clean to start with. Or maybe just a cold solder joint, that problem affects production lines as well as hand work. If a 3-wire connection really had a perfectly solid mechanical twist under the solder--it wouldn't have failed even if the solder had. Obviously the solder had not wetted out and penetrated the wires, making that a failure due to a cold solder joint.
And since it was in a hot rod--we have to assume the wires were all proper stranded wires, not solid ones, to begin with. Right? That would be another failure mode, regardless of connection type.