I've been around awhile and seen plenty of layoffs, layoffs are almost never about performance at the individual level.
It's nice to believe they are because in times like these thinking to yourself "I'm a least in the top half of performers" can give the illusion that you're safe. However, this thinking is ultimately harmful because when you or your friends and colleagues do get laid off you will continue this thinking and considering it a valuation of your self worth, or the worth of colleagues you respect.
You don’t lay-off 10% of your work force without need, and you don’t do it at random.
But at the same time, these are probably the same companies that say "competitive work environment" somewhere on the job application so maybe employees should expect it
Anecdotally, I've seen touchy feely corporate tone along with this strategy, and would suspect that is a fairly common combination. What you describe certainly exists, but it's not always so obvious.
At the end of the day the differences in employee performance just aren’t that big and everyone knows it’s hard to accurately judge.