I'd argue it shouldn't matter what the cause is. It's a little far fetched, but I could imagine teams organizing mechanical failures to gain an unfair advantage. All it would take is to tell the driver the wrong gearbox mode to cause a spin, Monaco style. As written it would suck to have an honest car failure and then lose extra grid places, but I think those kind of incidents will be pretty equally spread among the field.

it might be debated on who is the “sole cause”

Yes, the stewards will debate this.

I'm sick of these subjective expressions in the rules. They are reasons why some drivers seemingly get harsher penalties than others, and nobody can clearly explain why.

There isn't a debate though.

Adding that extra "technical issue excluded" Clause. is just extra complication that undermines the entire rule.

That's exactly what I was thinking too. It's a high, but subjective, threshold.

I'm glad they're seeing how this type of rule works in the feeder series before trying in F1.