Also, you're missing another obvious argument. Most tech companies that are doing layoffs could afford to keep their employees. Dropbox hasn't done 3 rounds of layoffs because they're on the verge of bankruptcy but rather they're just following the trend and pleasing shareholders or whatever.
So I'm not arguing for less jobs but rather less corporate bullshit.
How do you expect this to work? Companies hire because they think the extra man-hours is going to give them a competitive advantage. Companies agreeing not to compete each other seems suspiciously like a cartel.
That's still cartel behavior. If Google and Apple formed a cartel to fix handset prices, they could still theoretically compete with each other on features or whatever, but that'd still be a cartel.
All you are arguing for is that Dropbox should never have hired these people in the first place. Why is that better? At least these people got some years of high pay, experience, networking relationships, etc. Obviously it's disruptive, and it could be a big net negative for people who maybe jumped ship from more stable jobs only to be quickly laid off, but that's not the broad experience.