This is a terrible occurrence but it is not COMMON. It is really UNCOMMON. Not sure what your guy's definition of common is, but this does not happen often at any dog park I've ever been to. I've actually never seen something like this happen and have gone pretty consistently throughout my dog's first 2 years.
Sure...there have been fights, but they are not common. Maybe 1% of the times I've been to a dog park have I seen a fight, and I've never seen a dog get injured or hurt. I've seen plenty of stupid owners, most of the time SITTING on benches and just letting dogs do whatever they want.
If I were you, I wouldn't go back to a dog park. I also wouldn't just let you dog into a dog daycare without YOUR supervision. You need to find some obedience classes where you can socialize your dog in a very controlled environment (on leash and little or no interactions between dogs).