As I understand it - I was a bit young when it happened, so all I have are secondhand accounts - IE 5 on Mac was substantially better that other browsers due in part to its CSS support.

The chapter on IE for Mac in iWoz has nothing to do with how the browser render engine worked. It is about how the OS behaved after it was installed.

Tasman was way ahead of Trident actually. It had many problems Gecko had in that the web didn't care much for standards so implementing the standards, even well, wasn't considered a selling point. It was years of mostly Mozilla effort to make standards matter enough that web developers came around to them and then Tasman was viewed as an amazing pioneer alongside Gecko.