I believe expansion differential of aluminum and steel screws caused a return to copper. I lived in an aluminum wired house back in 1973 and there were lots of electrical problems due to this.
Local building codes were changed to require a “pigtail” on aluminum wire, to copper pigtail, to steel screws because of this.
Correct.
That could be. Just armchair quarterbacking.
Dissimilar metals can be problematic and cause corrosion and a destruction of the connector. Not only does it break down but it becomes resistive which means heat. Heat can accelerate the process. Heat can lead to fire.