My herding instructor doesn't allow dogs to beat up the stock either. But I have watched video footage of other dogs, with other sheep, and other instructors that are theatrical. Dogs slamming sheep all over the place, tackling/pinning them to the ground, chewing on them, and so on. Maybe these instructors are indulgent (perhaps because the student is paying, and they view the sheep simply as a widget?) or they just don't care. You tend to take a more personal view of the animal's welfare when you own and value them....
Some of the people I train with trial their dogs. Others are livestock owners/farmers training for specific important tasks. Me, I'm somewhere in the middle.
A correction (grip/snap/other force) should be used when necessary, and then end when the animal complies. Period.
To the OP, try and find an all-breed (maybe AKC or AHBA) trial, and go watch multiple breeds run on the same course, and you may see some differences. You could also go and watch an all-breed instinct test to see the raw tendencies of different, untrained dogs. It's very interesting, if the tester is genuinely interested in educating the spectators and explains what's happening.