At the expected odds on those 2 horses you would need to be right 90% of the time. Maybe 80% factoring rebates. Still not a good option
You assume every one of them is better every race. That is not true. These guys are using computers and are betting horses with low odds. I'll bet they are winning 80%+ of the time.
This wagering is probably causing the odds of the horses with high odds to pay more than they should when the come in.