About a year ago I read this and attempted to build a similar model (with more layers ;)) using data I scraped from Hong Kong Jockey Club’s website. Although I used much fewer features, it still produced profit in held-out races: https://teddykoker.com/2019/12/beating-the-odds-machine-lear.... Obviously there are many caveats when backtesting like this but I thought it was a fun project!
I had a coworker who would prepare for weeks for stakes races and follow a few second tier horses as well. Twitter made some aspects easier as there is a racetrack Twitter community. His specialty was identifying exactas where a long shot would place or win with a favorite.
He’d pay people to film workout at Belmont and Saratoga and tweak his model (an Excel spreadsheet) based on what he saw. He would have a sense based on the workouts, weather, etc and would pick 4-10 races a week.