HF trading is yes, almost fully automated otherwise it can't be called HF simply because human brain can't act as fast. You think MMkers are making money by trying to capture the spread of the underlying when the spreads are near zero across most markets (most popular ones anyway)? Dude, market makers can make money even if the spreads were negative (aka in favour of the client)
I think I can make money using only a DOM. But I couldn’t follow multiple ones. That’s why I would use charts. To keep up with several markets at once. A + is volume profile per price which TT added to their DOM. But I am not a Market Marker.
TT offers Premium Services which are available to all. Some market makers take advantage of these services like TT Prime for Autospreader. Other do not. It depends on their strategy. https://www.tradingtechnologies.com/infrastructure/premium-services/