This! It needs management people who understand their role as being "facilitators", rather than being "decision makers". And they are kind of rare.
Management are just as bound by the rules as non-management, or should be.
Of course, "reasonable" here has a strong subjective component.
I have seen dramatic change in an individual, but it's the exception. More likely is a slow progression to dismissal. This can be handled well by management with appropriate skills, but is hard and is a often suboptimal. However it's possible that this process is a necessity in any organisation that supports its staff. Wishing it to not happen is unrealistic, and indicates naivety. Perhaps these naive, disgruntled employees are part of a larger problem?
It's a boatload of work. Expect to spend as much time per week as you usually spend on 3-5 people. Then make the call if you can afford to do that. It's buying you a lot in terms of employee goodwill and team morale. (The second one only if you don't neglect the team over it, obviously :)
It is one of my signals of inexperienced management that they believe they can/should take on this sort of challenge.
Of course it's a judgment call. Some things, you cannot fix. But some things, you can, and the cost of doing so is much less than rehiring. Good management means making those judgment calls, not just saying "meh, I don't care about low performers, too much work".
Maybe, just maybe, that's a tiny part of the reason people on my team seem to stay longer than 4 years. Because we don't just treat them as disposable cogs.
And yes, not every situation is salvageable. Alas. Knowing when to stop is why I'm in favor of having a defined process well before you come to the "change, or else" part. That prevents the sad effect that your bar shifts as you collect reports, just because you've got more things to do.
1) believing you can dramatically change the performance of an employee -- it's very rare to save someone and less experienced managers always believe they can.
1.5) corollary to the above: not realizing the team is aware and waiting for you to fix the problem and won't thank you for taking longer to do what's necessary.
2) believing that people don't know what you're thinking -- people see you coming a mile off.
3) thinking you can wait to fix a compensation problem until the next comp review -- everyone waits too long on these.
4) believing HR when they tell you that you can't do something that's right for your team -- what they're really saying is that you have to go up the ladder until you find someone who can force them to make an exception.
5) not properly prioritizing the personal/social stuff -- at least this is my personal failing, and why ultimately management has not stuck for me.
6) believing your technical opinion matters -- I've seen way too many VP's making technical decisions that they are too far from the work to make, trust your team!
It'd be fun to see a list of these from the non-management point of view. I'd start off with the inverse of #6 above:
1) believing your technical opinion matters -- the business is what ultimately matters.