>You can tell them what they are doing well, what they aren't doing well, praise good employees and criticize bad managers.
You can do that over a beer or two with the (ex-)colleagues any time before or after you leave. It's not like you are forced to delete them from the contact list. And if you have managed to build this kind of trust between yourself and another employee, it's always a good idea to keep a connection to them. Ping them a couple times per year, discuss some common topics, and be ready to refer each other if one is looking for a job and the other one has an opening at their company. This is called "networking".
As far as the exit interview goes, the only things it's wise to say there are the same as telling your new employer why you left the previous workplace. "Just wanted to work with X, while they were focusing on Y, so we shook hands and parted". Everyone knows it's bullshit, but it's a test of your ability to de-escalate and avoid conflict, and it is very important.
Oh, and don't underestimate the bad managers either. If they abuse you and you still act professionally (and leave politely), you are just a resource. You are no longer needed, they have no interest in abusing you, they might even give you a neutral reference if anybody asks (although don't count on that). If you personally call out their bullshit in front of other subordinates, they may take it personally, and you really do not want a personal vendetta with someone who's full-time job is to spread gossip and manipulate people.
You can do that over a beer or two with the (ex-)colleagues any time before or after you leave. It's not like you are forced to delete them from the contact list. And if you have managed to build this kind of trust between yourself and another employee, it's always a good idea to keep a connection to them. Ping them a couple times per year, discuss some common topics, and be ready to refer each other if one is looking for a job and the other one has an opening at their company. This is called "networking".
As far as the exit interview goes, the only things it's wise to say there are the same as telling your new employer why you left the previous workplace. "Just wanted to work with X, while they were focusing on Y, so we shook hands and parted". Everyone knows it's bullshit, but it's a test of your ability to de-escalate and avoid conflict, and it is very important.
Oh, and don't underestimate the bad managers either. If they abuse you and you still act professionally (and leave politely), you are just a resource. You are no longer needed, they have no interest in abusing you, they might even give you a neutral reference if anybody asks (although don't count on that). If you personally call out their bullshit in front of other subordinates, they may take it personally, and you really do not want a personal vendetta with someone who's full-time job is to spread gossip and manipulate people.