In my experience, these slackers do exists in meaningful numbers (maybe most of PIPed but I know at least a few long timers). That said, an even bigger problem

In my experience, these slackers do exists in meaningful numbers (maybe most of PIPed but I know at least a few long timers). That said, an even bigger problem is that the majority of people are incentized to slack in some capacity. The impact & output of work within Google follows something like a perato distribution and yet the payscale is pretty flat. It creates this weird incentive system that almost encourages some base level of slacking unless you really want that promotion. And the difference in output makes it pretty hard to staff project and superstars often end up overworked which is hardly fair to the people doing the work. This wasn't always the case, but is probably the norm at larger companies. It does seem to me like the way comp is modeled isn't ideal, but I'm definitely not a comp expert. My guess is that more discretion in pay would open companies up to all kinds of legal liabilities not to mention actual unfairness. All that is to say that there is likely some extra slack that can be let go with little effect.