I am not sure about that one. Granted your are right on the DC multi stranded being for flexibility and vibration.
I theorize that it travels on the surface area of wires wither they are stranded or or solid would be application and I am not the only one on this theory as it has to push the valance electrons down the wire.

Current isn't concerned about wither its AC or DC. Its the flow of the electrons that matter. This is why with higher amperage loads, you need thicker larger diameter wires.

If the surface area or size exceeds the wire fuse amperage level what happens? It melts and opens up the circuit. Fuses are just melt-able links that are supposed to melt when the amperage exceeds the specified rating.

Granted temperature and resistance need to also be considered.

Could that particular theory be wrong.. possible but mostly when wires melt down the first that goes is the insulation then the wire itself which is due to heat resistance of materials used.

Plus they also seem to you really look closely burned from the outside in thus is to why I think this theory is correct. :-)

And Yes I know this Theory goes against the grain and everything says otherwise. As the standard has more surface area then the solid and this is why its a Theory. As solid wire is can't take heat then stranded can either.

So its possible its a bad theory and that does need to be mentioned on here so thanks Charlie.. :-)