So the question is can automotive wire be used safely? I think that depends upon what you are doing with it, although I wouldn't use it because of the weight.
I think the answer to the "safely" aspect is how well one understands the limitations of "commercial" wire, automotive or not. While there are commercial wires with similar performance characteristics to AS22759 wire, they end up costing about the same. We are talking about "cheap" wire, so typically PVC or some variant of insulation.
For example if you use wire with 85?C insulation in environments hotter than that, i.e., firewall forward, you can be pretty sure you have compromised the wiring. If the wire is required for continued safe flight and landing, safety for sure. The 85?C rating is not just the environment but the self heating of the wire due to current flow added to the environmental temp. This is why the minimum for aircraft wire is 150?C. The curves published for wire loading in AC43-13-1B are all based on 150?C wire in a 20?C environment. So if you use a lower temp rated insulation you have to derate the wire current carrying capacity and use smaller fuses or CB's for a given wire size. I have conducted actual wiring current carrying capacity testing for aircraft. Temperature is the limiting factor and is the limit is driven by the insulation's ability to withstand the elevated temperatures.
Then look at abnormal conditions- a wire overloaded due to a malfunctioning device or ground faulted in an arcing situation which doesn't blow the fuse or open the CB. Assuming that the wire is not Tefzel or similar material since you are trying to save money, the wire overheats and the insulation first produces copious amounts of noxious smoke, then it catches fire and burns really well. Since the fire is somewhere under the instrument panel or under your seat, you have no idea what fuse to pull to stop it. If the wire is in a bundle now the rest of the bundle is compromised and catches fire.
You are probably saying that this won't happen because you have fuses. But you used the fuses suggested by AC43-13-1B and so your wire is only protected from reaching 150?C. Your PVC wire is melted by then.
If you are IFR this is a serious situation likely to kill you, VFR is no fun either.
I know about a glider that crashed due to an electrical fire and smoke in the cockpit. Cheap commercial wire was used.
Would you say this affects safety?
AS22759/16 or /34 wire will produce limited smoke and will not sustain fire even if overheated severely.
A note on "teflon" wire. Pure TFE insulated wire is bad for general aircraft wiring applications. It resist high temps really well, barely effected by a burner flame, however pure TFE will cold flow when pressure is applied. Simply tying or clamping the wire bundles can cause pure TFE insulation to thin out at the pressure point eventually becoming so thin the insulating value is compromised. I did testing on that also.
Happy Thanksgiving to all.