Agreed. This is likely why 921 still states that research is still ongoing related to single-compartment fires (see 9.11.7.5.1 - 2017). In a single room, your appliance/electronic power cords are likely going to be your best locations of arc melting.

The time required to induce an arcing event on electrical cables was studied in "An Analysis of Heat Flux Induced Arc Formation in Residential Electrical Cables."

In summary, the results showed that in order for an arc to occur within a timeline of investigative interest (i.e. minutes versus hours), the cables must be exposed to conditions representative of flashover/direct contact with the hot gas layer/direct flame impingement. Computer modeling was also done to show that the room had to experience post-flashover conditions for several minutes before enough heat was transmitted though the gypsum ceiling under worst-case conditions.

However, this still does not mean that arc mapping can't be used at all, in residential or other settings. If you don't gather the data, you don't know how it can help.