2) Even today, bonds are traded OTC and mostly by people. In the 1990's, 100% of bonds were traded by people. Bond market cap dwarfs equity market cap.
3) Exotic OTC options were a big thing in the 80s and 90s. While that's not true today, when they existed, all of those were traded by people as well.
4) Most hedge funds today manage their positions with excel and trade based on analyst recommendations. They might have some fancy factor ops engine or something, but it's basically an after thought.
5) Around the dotcom boom, Goldman's equity desk had over 500 traders.
Fundamentally we are talking about a lot of different things. Different asset classes, buy-side vs sell-side, NYSE systems vs pit traders, etc etc. We can slice and dice these numbers in many different ways: total number of discretionary firms vs quant, trade volume vs assets, buy-side vs sell-side, etc etc. There's many ways to look at it that result in different conclusions. All I'm saying is that computerized trading is probably not yet the dominant paradigm and it certainly wasn't the dominant paradigm in 2007, much less 1990.