So, NJ, you've never seen the point of a multi billion pound industry? As for "It's quite obvious that some horses will be able to run faster than others", if you backed horses on speed ratings alone, you'd be on the streets with a mangy old mongrel for company sitting under a cardboard box. Tactics play a large part of determining which horses win on the day, much as they do in other sports.
No-one likes to see these beautiful equine athletes get injured but racehorses are bred to race. The clue is in the name. If you don't like watching it, you can always watch Peppa Pig.