"Due to both privacy and efficiency concerns, almost all Ethernets today are fully switched"

I don't think those were the reasons. The main reason I remember was cost. Shared media pretty much meant coax, and twisted pair is much cheaper. When switches became cheap enough and capable enough, the savings of running TP everywhere became the dominant factor. This also eliminated long cable runs and the frequent disruption of losing an entire segment at once, so reliability was also a factor, but IIRC those improvements were secondary in most purchasers' minds.

I guess cost reduction is a form of efficiency, but I certainly never heard privacy as a reason before.