Earlier quoted context omitted.
I agree, but I think what he's trying to get at is that designers were more politically engaged on the whole, especially during Modernism. However, it also had its downsides, the major being design hubris (e.g. over-planned cities, complete top-down organizational thinking, treating all people interchangeably, etc).
Right, and that is almost exactly survivor bias. It isn't that they were more engaged as a whole. The ones that we talk about were.
There were far less people who could call themselves designers at the time. It was a slower craft and took more training.
It's like in music. Yeah, there were other bands other than the Beatles and Rolling Stones, but it was harder to produce and distribute music back then. Thus, the industry was more monolithic than it is now. The ones we talk about now are more representative of the state of the industry back then than Lady Gaga (or whatever) is of now.