This is absolutely false, tech is a force multiplier in nearly every business even if it doesn't require onsite software engineers to get that productivity bump. Look at the Bloomberg terminal in finance, Salesforce/CRM in sales, Epic in healthcare, Westlaw in legal work, the list goes on.

Now a lot of the time, firms can get a better product by purchasing one than trying to build something in house (where anyone producing HFT tech won't sell that product because it's an immensely valuable trade secret). This said, I'm sure there are forms of intelligence gathering that is also built in house by firms that allow them to implement market beating strategies.