To be fair, there are also the interesting niche cases where someone is equally capable as Jim/Pam, but they're just not as good at selling themselves. Both cases usually more applicable to larger companies.
One thing that impressed me about IBM, during my brief tenure there after the Blekko acquisition, was that they had a very deep catalog of online self paced training material for developing manager skills. I don't know how many people availed themselves of that resource but since that time I have really wished I could have pointed people who were struggling at some of the courses they had.
Also a lot of people get really defensive and go into denial mode. Or are really full of themselves. People have a really hard time getting the straight out evaluation, or get despondent, and your manager is trying to give the feedback to the capacity level you have shown.
For context, and again I don't disagree here, I was using it in the sense of saying something that may be technically 'true' (didn't get the raise I hoped for) & (went to bat for you) but in context would give the opposite impression than the one you got.
Consider a company that has a 'mandatory fire the bottom 10%' and a manager who doesn't want to go through the effort to hire someone and so argues that they should be allowed to keep employee A even though they are their lowest rated employee (that would be 'going to bat for you') and it would easy to imagine the manager wasn't happy with their own raise, and "it's been a tough year" ? How? Tough to get stuff done with under performing employees or tough for the company?
So lying? Yes, all by omission. And of course some particularly bad managers just straight up make things up.
So employee B comes in and says, "Hey employee A makes 15% more than I do and we have the same job! I even have more experience!" And the manager rates employee A's performance above employee B's so the salary is "appropriate" considering their relative productivity.
The problem comes in when the manager can't have an honest conversation with B to tell them this, and instead in their review gives them lots of happy talk and makes some sorry excuse for the small raise (or no raise!) saying something like "It has been a tough year and even I didn't get the raise I had hoped for! I really went to bat for you but nothing I could do could move them on available compensation." When, in fact, that is a lie and the employee is just being gaslighted because the employee would be mad and upset if they told them the "truth."
A good manager tells their reports what is expected of them and how it is measured so that when review time comes they are both on the same page when it comes to their pay. It also helps with making actionable plans to improve.
Sadly, there are a LOT of crappy managers out there.