> there's usually another anchor point
The original design supposedly had two screws, but was manufactured with one. When you have two fasteners (typically nuts, as opposed to screws...) they can be mutually secured with lock wire. That is very common.
It is decidedly not common to lock wire electrical terminal fasteners in aircraft, or anywhere else for that matter. Typically lock washers and self-locking nuts are used. I'm not a certified aircraft electrical system designer, so I can't say definitively, but there are some pretty obvious reasons: First, these are typically small fasteners: lock wiring is hard enough on large fasteners. Lock wiring tiny little nuts with small gauge wire approaches the unreasonable. Second, lock wire is not insulated, so you would end up with a rats nest of exposed conductors leading to your terminals. Clearly unworkable. I suppose someone, somewhere has done something that involved insulated lock wire, but I've never seen it, wouldn't know where to buy it, and can't imagine how you'd employ it without abrading the insulation.
The problem here is the shared ground terminal. Stacking wires on ground terminals is common, stupid and a plague on electrical systems. The clamping force on a wire's ring terminal (and, thus, it's contact resistance, mechanical friction, ability to inhibit corrosion, etc.) is distributed among all of the ring terminals stacked on a stud, screw, whatever. Stack just one new terminal with another and you've cut the clamping force on both in half.
Half.
You are now the "engineer" and when someone dies as a result of your field engineered electrical system it's your fault.