8 or 9 years old is a ripe old age for a large breed working dog!
it’s really really SAD that anyone actually believes this. 8 or 9 is the prime of life for a well-bred, properly fed, properly exercised large breed working dog. An 8 year large dog may not be quite as fast or last quite as long in the field as a 3 year old, but the extra years of experience more than make up for the slight decline in physical ability. In other working venues a breed that took 2 to 4 years of expensive training to bring to full working ability that then “pooped out” at only age 8 or 9 would be considered a really bad deal.
That said, any hunt that just routinely killed their older hounds without make some attempt to re-home them needs to consider some other options. I can’t imagine any other working dogs that would just be killed and replaced; old police dogs and herding dogs generally stay with their owners in a state of retirement.